Short Barrel Rifle Loads

[Newts]

I had a quandary come up.

I have a short 18" barrel 7mm-08. With factory loads and my hand loads, I get significantly reduced velocity numbers. Which I do understand that is a given and am ok with it.

The question that came to mind the other day is if I would be better off focusing on heavier bullets or lighter bullets to get the most out of this gun. In that question to myself, the quandary came up - which(if either) bullet would generate the best velocity ratio for the load?

In other words, which bullet, heavy or light, would have the most grain to fps ratio?

I have read that in handguns you get better velocity per grain with heavier bullets because the heavier bullets have a longer barrel dwell time and therefore have more time for pressures to build behind it - or something to that effect. I just read it, not saying I believe it.

Is this the case, or something similar, in rifles also?



Senario based on Hogdon data - 24" barrel;

130gr velocity is 2950fps

150gr velocity is 2700fps

With my gun;

130gr velocity is (?fps)

150gr velocity is 2550fps


Given that scenario, my gun is losing average 25fps per inch of barrel. Would that(should that) also apply to the 130gr bullet? So would I expect to see 2800fps from the 130gr bullet?

Hope this makes sense what I am asking. Just a curiosity. I know I can try it and see the results, but I just wondered if anyone had ever done it before and got a good idea based on a variety of different firearms.

[Six Pack]

Based on the old rule of thumb that has been around longer than I can remember, you will lose 25-50 fps for every inch difference in barrel length. Looks like you are in that range so I would expect the same for the 130g bullet.

In my experience, you should have a similar ratio with the lighter bullet from the shorter barrel. However, there are other considerations. Are you hunting or punching paper? If hunting, your max realistic range is probably noticeably less so now you have to consider terminal performance of the bullet.

If it were my rifle, I would probably load a good cup and core 140g bullet close to max and limit my range to 200 yards or less. But, hey, that's just my occasionally humble opinion.

ETA: and, yes, I load for three different 7-08 rifles...none are short barreled. My preferred bullets are the 140g Nosler Partition and the 139g Hornady. All shoot equally well with Big Game or H4350.

[CarJunkieLS1]

Load the 130 Speer BTSP those are a very accurate bullet and in gel expanded at 1975fps and penetrated 21" of ballistic gel. Has a fairly decent BC too.

[Newts]

Originally Posted by Six Pack

Based on the old rule of thumb that has been around longer than I can remember, you will lose 25-50 fps for every inch difference in barrel length. Looks like you are in that range so I would expect the same for the 130g bullet.

In my experience, you should have a similar ratio with the lighter bullet from the shorter barrel. However, there are other considerations. Are you hunting or punching paper? If hunting, your max realistic range is probably noticeably less so now you have to consider terminal performance of the bullet.

If it were my rifle, I would probably load a good cup and core 140g bullet close to max and limit my range to 200 yards or less. But, hey, that's just my occasionally humble opinion.

ETA: and, yes, I load for three different 7-08 rifles...none are short barreled. My preferred bullets are the 140g Nosler Partition and the 139g Hornady. All shoot equally well with Big Game or H4350.

Thanks.

My scenario was just hypothetical, meant to illustrate what I was thinking. I have not chronographed my loads yet so I cannot compare to published data.

One thing I have also heard said before was that the fastest powder in a long barrel is going to be the fastest one in a shorter barrel. Simple looking at hodgdons site, comparing their pistol data in 7-08 and rifle data in 7-08, shows that is not so much the case, at least not in a linear progression. The faster powders are real close to having the same velocity as the slower powders in a pistol but fall way behind in a rifle.

Not only that but the heavier the bullet gets the worse and opposite direction takes place in rifles vs pistols.

I don't doubt that for the most part there is not much difference, but maybe there could be an advantage to using heavy vs light as far as efficiency goes. Of course, I'm just speaking of strict powder to velocity efficiency, not talking about the right bullet for the job at hand. Think of it as just target work.

[TX Nimrod]

This subject was defined over 30 years ago by handgun silhouette shooters. The trends were:

1) the powder which gave the highest velocities in a long barrel almost always gave the highest in short barrels

2) heavier bullets lost the least fps going from long barrels to short barrels

That said, slow powders will give greater muzzle blast and flash. And heavy bullets generally will give less expansion in short barrels. For a hunting rifle, bullet performance is more important than efficiency or velocity.


.

[Doyle]

Newts, I used to hunt with a guy who had a copy of Quickload. He used that to play around with different powder combinations for a 18.5" barreled .260 that I had. You're right that nothing seams to be linear. What we found out was that QL predicted that RL-17 would give me the best combination of velocity and burn completion. I loaded up a half dozen or so but I moved away from him before I could do any further research and I never had access to a chrono to actually measure performance.

[jmr40]

Don't over think this. As long as your bullet impacts at around 1800 fps or more the bullets will expand. The difference is that the 24" barrel will retain the 1800 fps threshold about 50-75 yards farther down range. Instead of having a 500 yard gun you'll have a 450 yard gun. At 300 yards the slower round will have about 2" more drop.

This is a very complex issue. Until you actually chronograph some loads none of this means anything. I think you may well do much better than you think.

I don't load for 7-08, but some observations I've made with 30-06 and 308 from various barrel lengths.

* The powders that gave the best speeds from 24" barrels were also the fastest speeds from 18-20" barrels.

* I saw less difference in lighter bullets than heavy bullets from shorter barrels.

* The difference between 2 barrels of the same length is often far greater than the difference 2" of barrel makes. One of my 30-06 rifles, the Winchester (both with 22" barrels) is consistently 60-90 fps faster than the Remington. The heavier the bullet the bigger the gap. A friends 22" Remington 30-06 is 130 fps slower than my Winchester with the same ammo.

I have several 308's. Two with 22" barrels and the Winchester is consistently 20-30 fps faster than the Kimber. One, a Ruger with an 18" barrel and is only 50-60 fps slower than the Winchester, only 20-30 fps slower than the Kimber with a 22" barrel.

A lot of people think going to a faster burning powder will help a shorter barreled rifle shoot faster. Actually even the slowest burning powders burn up within 4-6" of barrel. Faster burning powders do help with handguns, but not with rifle barrels. Possibly with some of the short barreled rifles that are not legal to own unless you get permission from the government.

You might want to try a slower burning powder, especially with heavier 150 gr bullets. My data shows 2750-2800 fps is possible from a 24" barrel. You won't get that, but you might just get 2650 from your 18" barrel with the right powder.

[44 AMP]

Unless and until you chronograph the ammo you are using in your rifle, from your rifle, you are only guessing. Probably close to what the factories say and what testers get on their websites etc., but not guaranteed to be so, and while uncommon its not unheard of for your rifle to give you velocities quite different from what you expect to get.

A friend of mine was quite happy with his .270 Weatherby Magnum, he had a 26" barrel and knew he was getting the highest speeds there were, until he got a chronograph.

AND then discovered that his 22" Win .270 was shooting 30fps faster than his Weatherby. With a shorter barrel and using less powder...

Every rifle behaves a little differently, some much more than others. The stars lined up, my friend wound up with a "slow" Weatherby and a "fast" Winchester. Two other individual rifles might (and probably would) have been the opposite.


SO, no matter who tests what, and says what you ought to get, you don't know what you really get from your gun, until you test IT.

[Unclenick]

What the last two posts said mainly covers it. The only minor point of disagreement is the idea the powder is all burned in 4 to 6 inches. It's not. Pressure and temperature drop rapidly after the peak, slowing the burn rate of the remaining powder way down. Powder that is still burning plays a big part in muzzle fireballs. Indeed, the reason the military raised the pressure of the new(ish) 5.56 M855A1 EP round to over 65,000 psi is because they decided to achieve their target velocity with a faster powder to cut down on the amount of muzzle flash from the M4 and other shorter barrel weapons.


Newts,

I don't think you're really asking a question that has an answer without more constraints. If I choose a very fast powder, I will find I get the most fps/grain with a pretty light bullet. If I choose a very slow powder, I will find the lightest bullet doesn't offer enough reaction force (inertial resistance) to burn it well enough and I can get more fps/grain with more bullet weight up to a point. Beyond that point, additional bullet weight will make velocity drop again. With extreme weight (whole barrel filled by the bullet) the gun will just burst before the bullet moves appreciably.

[Charlie98]

I had the same issue with my 20" .348WCF model 71. Using a slower powder (H4831) I got a huge muzzle blast but reasonable velocity... or so I thought. I worked up some tester loads with IMR3031... what was a starter load actually gave me higher velocity, way less muzzle blast, and better accuracy. Yes, this is anecdotal evidence, but my point is you probably have to fool with different powders for any particular bullet weight in any particular barrel. In hindsight, H4831 is probably a good powder in the .348... with a heavier bullet and a longer barrel, it just didn't work for my particular setup.

I bought a .45-70 single-shot from a friend of mine, while talking about load workup, he cranked out some load data on his QuickLoad program. One of the more interesting features for any load and firearm combo is 'percentage of powder burn.' I found it fascinating that even in my 32" barrel, a relatively fast burning powder (AA5744, IMR4198) under a heavy (405grn) bullet does not burn completely... not even 90%. It isn't until you go to a relatively faster powder (2400) that you get an almost (99.6%) burn, or faster yet (Unique) where you get 100%. Oddly enough, and this is certainly a product of pressure and burn characteristics, the larger the charge, the higher percentage of powder burn; but certainly there is a point where that would peak and reverse, theoretically, anyway.

[Unclenick]

For a 32" barrel, have him turn QL's optional bore friction to get a more accurate result.

[Charlie98]

The 'friction-proofed' box is not checked... I'll have to axe him!

[Unclenick]

The friction-proof allowance reduces the start pressure for moly bullets or other coatings. The bore friction is on one of the drop-down menus, above. I'm not on my QL computer right now, so I can't check which one.

[Newts]

Thanks for all the replies. I decided to focus on the lighter bullets. Got a good deal on several of them, and since I have the 308 to poke around with heavier bullets, the lighter ones get the nod.

I’ve done some testing and have come up with some interesting results. Not done entirely yet though. I’d like to ask some questions about my testing but figure it’s better on a different thread. I’ll update this one once I get some more testing done.

[FrankenMauser]

Fairly well covered above.

In theory, a heavier bullet will do better in a shorter barrel, since it will accelerate more slowly and have more time to be accelerated. However, that doesn't seem to always be the case in reality.

I just wanted to hit this point, real quick:

* The difference between 2 barrels of the same length is often far greater than the difference 2" of barrel makes. One of my 30-06 rifles, the Winchester (both with 22" barrels) is consistently 60-90 fps faster than the Remington. The heavier the bullet the bigger the gap. A friends 22" Remington 30-06 is 130 fps slower than my Winchester with the same ammo.

...Yep.
My Ruger 77 Mk II .270 Win has one of the slowest barrels I've ever encountered for a .270 Win. I'm down on velocity (130/140 gr bullets, real world, chronographed velocity with the same loads) by 150-200 fps, compared to another that I owned, and nearly all others in my family.
It's just a "slow" barrel.

However...
I had the barrel chopped from 22" to 18.5", to be threaded for a suppressor last year. I lost less than 40 fps. (I think the exact average was 31 fps, but can't find my notes.)
...Which is right about where any other .270 Win should end up with a 18.5" barrel. (.270 Win loses about 35-40 fps per inch, from 24" to 19".)

I evened the playing field by chopping the barrel.

[603Country]

The OP should just shoot the 130’s. Simple.

[FITASC]

My model 7 with the same barrel length really prefers the 140 gr bullets, both Sierra and Nosler.