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Discussion Starter #1
I know that a shorter barrel is going to give you less velocity than a longer barrel and that the actual velocity loss can have a greater or lesser effect depending on several factors. But it's turning out to be a topic that I don't see discussed much except in bits and pieces that are dang tough to put together. As an example, here is what I am trying to research right now...

Just for the sake of discussion and not to get into the best bullet/powder debate... For a .308 load, two very commonly mentioned loads are Sierra 155 Palma over Varget and Sierra 175 MK over 4064. Using the manufacturers max loads for these two charges gives me 2909 and 2728 fps respectively. What that data does not state is for what barrel length.

If I assume that the data is for a 24" barrel and I have a 20" barrel, I can expect lower velocities. I have found the necessary formulas for calculating what the expected loss will be, but before I break out the slide rule and abacus, here some questions someone here can probably answer.

Is it worth going to all the bother to calculate if there is more or less loss between the 155 and 175 gr bullets or just estimate it as 20 fps per inch and be done with it?

How much effect does the burn rate of the powder have in all this? Would a faster powder be better in a shorter barrel or wouldn't it matter?

Am I into the realm of "angels dancing on the head of a pin" here?
 

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I know what you mean about short barrels, loads, and finding data. I was considering going from 20 to 18 and have been looking into this as well. In the end I came to the conclusion that it simply comes down to personal taste and what your rifle likes.

I haven’t found a big difference comparing 24 to 20 Inch barrels. When you start to chop to 18 or even 16 inches that is where velocity really starts to change.

From what I have read, there can be huge difference between 155 and 175 gr bullets: 155 can be up at 2900 fps, while 175 will be around 2500 fps out of a 20 inch barrel. Similar to your own finding. I don’t believe these would be considered ‘hot’ loads, although you mentioned loading to max. I regularly shoot 180’s out of my 20 inch rifle and they do fine- averaging about 2600 fps with 44 grs of Varget. This isn't a hot load at all.

As far as faster powders, I like Varget. It is pretty fast, but its consistency over different temperatures is why I stay with it. You really can’t go wrong matching Varget to a 308. R15 is also very popular, as it tends to be a bit faster, but is also more sensitive.

When I was researching I copied all the interesting data and tips I found into a document. It’s all quotes gleaned from various forum threads. I can add it to the thread when I get home. Might be useful to have some of the information in one place since so many are using short barrels now.
 

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Discussion Starter #3
Northerner said:
When I was researching I copied all the interesting data and tips I found into a document. It’s all quotes gleaned from various forum threads. I can add it to the thread when I get home. Might be useful to have some of the information in one place since so many are using short barrels now.
Thanks. A lot of the best information I have found is geared to things like Palma rifles being loaded single shot into honking long barrels. And I know that once you start shrinking the bullet down to magazine size and a short barrel, everything changes.

Ultimately it all comes down to time at the reloading bench and the range to find out what works for me. But there's no substitute for understand the theory behind things to start with.
 

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You will lose some velocity going from 24" to 20" barrel but the best thing for you to do is get a chronograph and worry about what your rifle barrel is doing. Those numbers listed in manuals are very generalized and shouldn't be used for anything but a vague idea as to where you might be.

There are no hard numbers of how much velocity per inch as every barrel is different. Here's an interesting post by someone over at the Hide with some data from his rifles:

I recently had the opportunity to shoot 3 different Rock River Arms LAR8s with different barrel lengths.(16 inch CM, 20 inch SS bull, 26 inch SS Bull)
Rifles were like new with round counts between 3 and 333.
All shots fired flawlessly from a 5 round magazine.

5 shots were fired with each of 3 loads from each rifle
(41 degrees F, Chrono at 10ft)
Winds were EXTREMELY erratic creating obvious grouping issues. Despite this, all 9 of the 5 shot groups averaged 1.1 inches at 100yds. (many groups had 4/5 shots around .5)

Loads were as follows-
168 HPBT (bought as "BH factory new" but pulled down to reveal fired brass and 41.7gr of extruded powder w/a gold primer)
16 ave vel 2310 ES 88
20 ave vel 2416 ES 31
26 ave vel 2558 ES 39

155 Amax (Lapua brass, 45.6gr Varget, CCIBR2)
16 ave vel 2563 ES 10
20 ave vel 2644 ES 42
26 ave vel 2788 ES 58

175 HPBT Black Hills Factory (Red Box)
16 ave vel 2437 ES 141
20 ave vel 2465 ES 123
26 ave vel 2615 ES 103

Velocity loss per inch of barrel length was as follows-
26 vs 20 inch barrel
Average of 24fps (24 with 168s, 24 with 155s and 25 with 175s)

20 vs 16 inch
Average of 18fps (27 with 168s, 20 with 155s, 7 with 175s)

26 vs 16 inch
Average of 22fps (25 with 168s, 22 with 155s, 18 with 175s)

The ES were extremely high.
The 155 Amax load was chronographed over the summer in the 26 inch barrel and showed ES about half of what was experienced this time.
A larger sample size is obviously needed for more meaningful data!
 

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Great post Rob.

Here are the notes I made,

To be clear: All of the following are random snippets of posts from here and Sniper’s Hide concerning ‘Preferred Loads for Short Barrels.’ I made this to help me draw my own conclusions about what can be expected from short barrels and have an idea of the best place to start experimenting with loads. There are often no user names attached or sources, but they have all come from longtime posters and people who I have found to provide valuable and solid information. Nevertheless, it is still information taken from the internet so here is the necessary warning….

Please be careful using any loads that follow and start with lower charges and slowly work up.

I repeat, none of the following information was written or tested by me.
---

16 inch: The load I elected to use was the 155gr AMAX load from HSM. It has an advertised velocity of 2875 fps and is loaded to the HSM match specs. For this particular load, I measured just a tad over 2800 fps with our chrony 10' from the muzzle. I decided to use the 2800 fps number for our BDC with the published BC from Hornady of .435.

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Rem 700 SPS with a Factory 20" Barrel with a 1:12 Twist Rate.

Factory:
Federal Gold Medal Match 175 - 2,534-2,545 fps (5 rounds)
Handloads:
Using a 175 Grain Sierra MK Bullet
Handload - 2.800 OAL Loaded in Federal Brass with 210M Primer
44 Grains of Varget - 2,579-2,598 fps (10 rounds)
45 Grains of RL-15 - 2,627-2,648 fps (10 rounds)

Factory:
Federal Gold Medal Match 168 - 2,627-2,642 fps (5 rounds)
Handload:
Using a 168 Grain Sierra MK Bullet
2.800 OAL Loaded in Federal Brass with 210M Primer
44 Grains of Varget - 2,584-2,603 fps (10 rounds)

44-45 Grains of Varget or RL-15 is pretty much the magic number, and velocity will typically run 2,550-2,650 fps based on my experiences.

For a 175 Grain SMK you want at least 2,500 fps for 1,000 yards, which will give you:
1000 Yards = 43.00 Elev / 10.25 Wind @ 10 mph / 1,161 fps

For a 168 Grain SMK you want at least 2,750 fps, which will give you:
1000 Yards = 39.25 Elev / 11.00 Wind @ 10 mph / 1,140 fps
Good Luck getting 2,750 fps, reality is with a 168 you are looking at about 900 yards max to keep it supersonic.

-

I am getting 2700 FPS with FGMM 168's out of my 20" barrel. Accuracy is not an issue.

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With my Tac Ops X-Ray 51 with a 19" barrel with FACTORY Fed Match 168's ammo I am getting 2720. That was with a temp. range 60.1 & 99.3 degrees over a year. That was three dif. lots of factory ammo. When I hand load 155's lapua scenar's I get 2950. Will not give out the specs because its a compressed load ,not for the public forums. Its reloader 15 with Win brass Fed 210 Prims. & O.A. of 2.810. This is with Tac Ops Special reamer and the barrel is a Krieger 1-10. At 2950 the groups are just about 1/4 MOA. I use the Factory Fed Match most of the time because I can shoot below .100 with out a problem.

-

Somewhat to Fabro’s defense,

If my knowledge base was limited, and I did not know the source of the info, I would also probably throw up the “BS Flagâ€
 

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I have tired to push my 20 inch 308 past 2600 but it just doesn't like it ... it can do it with showing pressure signs but it shoots like arse. 2530 to 2545 ish is where it "happy". Now for reference purpose only I plan on shooting that load out of my 26 inch when it gets to above arctic freeze, side by side to compare velocity change. Ill post the numbers once I do. My big target 308 has a 26 inch barrel just because I wanted to push the 308 round and see what I can get out of it, just for fun. The 20 inch is a utility rifle that gets used for hunting as well so Im not trying to get to 1k with it. For reference I shoot 175 SMK over RL15 in my 308's but plan to test some other powders in my 26 inch.

Good quality discussion with solid info, hope to contribute some numbers next trip to the range. I even fire formed some Lapua brass to the 20 inch for the test.
 

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Discussion Starter #8
Doing some research into the notion that a faster powder might be better in a shorter barrel, I ran across two powders that might be worth further research.

Using the data from Hodgdon:

H4895 Max 46.0gr 2,804fps Burn Rate 87
IMR4895 Max 47.5gr (C) 2,897fps Burn Rate 89

By comparison:
Varget Max 47.0gr (C) 2,909fps Burn Rate 99

At least to my limited understanding, it might be worth trying H4895 because it is a faster powder and is not compress at the published max charge.

Now, what am I missing in this?
 

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Discussion Starter #9
OK, here is another really oddball question pertaining to barrel length...

There's been a lot of discussion recently about .308 155's, but these are designed to meet the needs of Palma shooters who have a bullet weight limit and who typically use very long barrels and shoot single shot.

A 20" barrel, on the other hand, won't be able to develop the velocity the long barrels can regardless of the powder used.

This then leads back to the question of bullet weight. Will a light or heavy bullet work better with a 20" barrel?
 

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Was thinking of experimenting with 168 AMAX's. While reading, I came across this old thread.

Gsmithpln (are you still around?), that's a good question with no straight answer to be found- I've been looking. Here are my thoughts after much reading. When this theme is discussed the same four facts always make an appearance:

#1- Bullet weight is directly related to barrel twist.

#2- Bullet weight is directly related to distance of target.

#3- Barrel length is directly related to muzzle velocity.

#4- Different rifles like different bullets, even if they are the same factory gun

I'm going to ignore #4 though. While there may be some truth to it, there also seems to be a lot of people having success with the same bullets. I think a rifle's preference may have more to do with the person who is shooting and/or loading.

As for the other three facts, It is rare they are ever interrelated. I have not seen anyone post the “ideal 18 inch 308 barrel” ie: “1/10 twist optimized for 175gr SMK for 900 yard shooting” or “1/11.25 twist optimized for 168gr SMK for 600 yards shooting” (I made these up). Typically people treat the facts as outlined above: They separate them. ie: “If your going to be using a 180gr bullet go for a 1/10 twist,”or “If you want to shoot to a 1000 yards get a 24” barrel.”

I have also noticed a trend towards the 175/178gr bullets being recommended as the 'do everything' bullet. This is with good reason as most people find them easy to load, accurate out to 1000 yards, and not overly sensitive to wind. So the logic goes: Why pick the 168gr if the 175/178gr projectiles will do everything the 168gr's do and more. This is sound logic, but maybe the 168 shouldn't be totally dismissed.

The 168gr round is known as an 800 yard round because after this point it starts having problems remaining stable. While there are marksmen that have had success shooting to 1000 yards with the 168, it is not generally recommended for this purpose. The same goes for 18”/20” barreled 308's. There are many videos and testimonies of success at the 1000 yard line, but most will agree it's not the preferred tool for the job.

So from this information it would seem that there may be a case for the 168 in short barreled rifles. A mid range bullet for a mid range barrel?

What I also think is interesting is that Tactical Operation’s rifles are optimized for the 168gr bullet. They are also short barreled 308's (18” to 20”). For those not familiar, see the Tango Series here: http://www.tacticaloperations.com/tangoseries/

It goes without saying that these rifles are machined at a far superior level than any factory offering, but I don't think that is relative to the discussion. What is important is that they are short barreled 308's and for some reason a very knowledgeable group of people decided to build them to shoot the 168gr bullet instead of the 175/178gr. No reason is given in the articles as to why this round was chosen, but while reading the article section (http://www.tacticaloperations.com/articles.html) the following caught my attention:

“This brings up an obvious question -- how short is too short? What sacrifices, if any, are made by going to a shorter barrel?

To answer these questions, we must first start by taking a look at the subject of internal ballistics. Internal ballistics is a very complex subject. There are many factors which affect the internal performance of a given cartridge and bullet. Factors affecting internal performance include the powder chamber capacity; load density; amount and burning characteristics of the propellant powder; temperature of the propellant prior to ignition; uniformity and speed of ignition; diameter, weight and bearing length of the bullet; and the length of the barrel and its interior dimensions

(http://www.tacticaloperations.com/swatd ... index.html)

Can it be concluded that the 168 is the ideal weight and size for optimum performance in a short barrel? It is established that LEO typically engage targets between 100 and 200 yards, so it would make sense they would choose a tool purposefully developed for accurate short and mid range work.

As for civilians, the 168gr also makes a good hunting round, as it is heavy enough to terminate just about any beast found in North America. This would allow it to share with the 175/178's the title of “do everything bullet,” - as long as its limitations as a mid range tool are respected.

I am by no means an expert, just trying to make sense of all the information I've come across. It would seem, to me anyway, that the 168gr is a good place to start.


As an aside- It would be interesting to learn what twist the Tac Ops barrels are. I've only seen the barrel description as “Proprietary chrome-moly or stainless steel Krieger.”
 

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Re:

Rob01 said:
Here's an interesting post by someone over at the Hide with some data from his rifles:
<snip>
155 Amax (Lapua brass, 45.6gr Varget, CCIBR2)
16 ave vel 2563 ES 10
20 ave vel 2644 ES 42
26 ave vel 2788 ES 58
<snip>
Velocity loss per inch of barrel length was as follows-
26 vs 20 inch barrel
Average of 24fps (24 with 168s, 24 with 155s and 25 with 175s)

20 vs 16 inch
Average of 18fps (27 with 168s, 20 with 155s, 7 with 175s)

26 vs 16 inch
Average of 22fps (25 with 168s, 22 with 155s, 18 with 175s)
This data is OK for what it is. But it would be extremely useful if the 155s were placed on top of 47.8 gr Varget and had a MV around 2950 for the long tube. As it is, it is not surprising that the delta-MV was low given that you weren't burning that much powder in the chamber.

That is, I happen to believe that MV loss per unit barrel length is dependent on how hard one is pushing the pill.
 

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Discussion Starter #12
Northerner said:
Gsmithplm (are you still around?), that's a good question with no straight answer to be found- I've been looking. Here are my thoughts after much reading. ...
My access to distance shooting is extremely limited and my time has been even more limited this year so I only have one good case study.

I did get the H4895 powder and already had some Varget on hand. I found someone with a cache of Nosler 155gr bullets so I decided to give them a go. The BC is not as good as the SMK, but the max distance I was going to be able to shoot was 600yds, so what the heck.

I tested both powders with a range of different charges and consistently found that the H4895 gave me better velocity for less powder and with a better SD. I took these with me to a three day precision rifle course at my favorite training facility in WV. We shot quite a bit under varying conditions from prone to barricade to step wall to moving targets and this load performed like a champion the whole time. The accuracy was extremely good and I was consistently using a much lower come-up than the folks shooting the standard Federal Gold SMK 168gr loads. I might also mention that by Sunday it was up to 92 degrees shooting in a limestone quarry and everything (including the ammo) was cooking in the sun.

I may well go back to using the 155's but I'm going back to WV in a couple months and am going to take some of the Hornady 178's with me and see if I can push them out to 1000yds.
 

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Discussion Starter #13
At the risk of belaboring and confusing an already complex topic, here's another twist. I ran through a ladder test using the Hornady 178gr Match bullets over H4895 in my Rem 700 SPS Tac 20". I'm pleased with the results but am a bit concerned by something I had not considered.

I have been so focused on the effect of the barrel length on the performance that I have not really carefully looked at the twist. The twist on this barrel is only 1:12 which makes me wonder if I might be pushing the envelope a bit with these longer bullets. They certainly are not as long as the VLD's but I don't want to spend a lot of time developing a load for a bullet that won't be any more stable at 800-1000 yards than my current 155's are.

There seems to be enough people using 175gr SMK and 178gr AMAX in this barrel that if there were any huge problems, they would have come up by now. But I also know that a lot of the "field reports" out there are for people shooting 100-300yds.

Anyone here have some good first hand data with bullets in this range in the 800yd+ range?
 

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If I understand you correctly...

...you're thinking about this bassackwards: A bullet with enough spin to be properly Gyro stabilized at the muzzle will have MORE than enough to be fully Gyro stable for it's entire journey back to the earth 4000 yards later. This is because the friction on the front of the bullet slowing it's forward speed down is proportionally much greater than the friction slowing it's rotational velocity.

The dynamic stability problem at long range comes from some other factors depending on the bullet, but not from too little spin. In fact, as the bullet slows and the frictional forces acting on the sides and nose of the bullet are lessened, the axis of rotation can actually be TOO strong for some bullets to track properly with trajectory.

But that's another ball of tea.


I'll add more to this later, if it hasn't yet been..
-Nate
 

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Discussion Starter #15
natdscott said:
...you're thinking about this bassackwards:
That's been known to happen on occasion. I can also over complicate a PBJ sandwich, but that's a different topic.

To rephrase. Longer (heavier) bullets like a faster twist to stabilize. Some sources recommend a 1:10 twist for 175gr bullets but I'm loading 178gr for a 1:12 twist. If I am not getting enough spin with a 1:12 twist, is it likely to show up at 100yds or might I not be aware of it until the bullet is further out.
 

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What I was saying above is that, if it isn't keyholing at 100 yards, it will NOT be keyholing at 1000 yards due to a lack of gyroscopic stability. That is not the same as being dynamically stable... It can be tumbling at 940 yards, but still have plenty of rotational axis rigidity from spin.

Some other explanation:

As temperatures drop, contrary to popular opinion, most rounds become LESS stable:

-Temperatures falling causes a slower rate of burn in your powder, thus lower MV, and resultant reduction in RPM.

-MORE importantly--and this one's big--as temperature falls, (and/or you reduce your altitude and/or increase barometric pressure) the bullets become less stable due to a change in the overturning moment: As bullets get longer and more pointed, their in-flight center of pressure is moved farther and farther aways from the center of gravity. This difference requires more and more RPM (and by proxy, twist rate) to keep the point-forward orientation. Since higher density air exerts a greater force on the front end of the bullet, (for the SAME RPM you generated with your rifle back at the firing line), it causes the bullet to be more likely to reverse orientation to what is naturally stable (weight forward).

This is the same pricipal as why rifle bullets yaw catastrophically when entering hugely more dense mediums such as water and flesh.

This is related to the reason militaries are so conservative with their twist rate selection: e.g.: the 7-twist 5.56 NATO is drastically more than is required to stabilize the 62-grain Penetrator. They need to be absolutely CERTAIN it will be stable down to 40 or 50 degrees below zero at any elevation on the planet. IIRC, They use a minimum spec of 1.7 Stability factor. Amongst a couple other reasons involving grunts and chrome, that would be why the M-16 mostly shoots like crap with almost any commonly issued ammo.

End of this is that, "No the 12-twist is not best used with bullets of that class", but it may work if you push hard and have the right conditions. Just shoot them, and if they punch oblong holes at 100 yards, then stop shooting, and give the rest to me or Adam. We're easy to get along with.

:wink:
-Nate
 

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avolcek said:
Also, wasn't the 1:7 selected not so much for the 62gr SS109, but for the M856 tracer...not that the whole 2gr difference is much.
Nah, the steel core of the SS109 requires a MUCH higher rate of spin to stabilize than a typical lead-core bullet. I'd think the tracer would probably stabilize at 10. Certainly 9.

Whatever the reason, they shoot mostly like crap...with any of the issue rounds. Breaking the 1 MOA barrier is usually possible with rifle-matched handloads using 69SMK or better.

But the 1:7 battle gun won't ever have any GYRO trouble!

-Nate
 

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Discussion Starter #18
natdscott said:
End of this is that, "No the 12-twist is not best used with bullets of that class", but it may work if you push hard and have the right conditions. Just shoot them, and if they punch oblong holes at 100 yards, then stop shooting, and give the rest to me or Adam. We're easy to get along with.
Thanks, that more or less goes along with what I had been wondering. I have a good load working with 155gr bullets, so it might not be worth the time and effort to develop a load with a 178gr bullet that may turn out to be marginal at distance under some conditions.
 

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Discussion Starter #20
natdscott said:
End of this is that, "No the 12-twist is not best used with bullets of that class", but it may work if you push hard and have the right conditions. Just shoot them, and if they punch oblong holes at 100 yards, then stop shooting, and give the rest to me or Adam. We're easy to get along with.
Well, it doesn't look like I need to give them (178gr Hornady Match) away yet. I took 5 different loads to the range and put them over the chronograph and shot some groups at 100yds. The higher velocity loads had better SD's and grouped quite well without any signs of keyholes. I'm not the best shot on the block, but I was getting 1/2" three shot groups and a 1/4" group. Now I need to get someplace that has some distance and check them against calculated drops.
 
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