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Powder: Gas gun vs bolt gun

H

Howie Feltersnatch

Deep in my Plums.
Full Member
Minuteman
Aug 9, 2007
332
10
40
Largo, FL.
Please read the scenario I personally encountered:

I performed the ladder test to develop a load for my LR308. According to the Sierra loading manual for the 168gr. SMK the load spread I had was between 39.7-44.7 (not sure on decimals...I don't have the book here with me) of IMR 4064. So I loaded 17 rounds raising the charge incrementally by .3 grains. My last round I made was 44.6. So off to the range I went.

I shot sight in rounds and then started the ladder test. It was shooting great and then the second from the last round, 44.3, it locked the action up. I fired the round, but the carrier didn't do anything. It didn't eject the old shell and didn't reset the trigger, etc. It absolutely locked up my rifle. I took it inside to the range gunsmith and he couldn't get it out. While I was explaining what I was doing and what I was trying to accomplish he told me I was dumb for performing the ladder test and that I need to read a book. I immediately let that fly through one ear and out the other.

He also said that I should not run rounds as high as that in a gas gun because gas guns can't handle as much a charge as a bolt gun can. Is there any validity to that?

What had happened (hindsight) to my rifle was the blown out primer from my 44.0 round got lodged in the locking lugs while loading in the 44.3 round that when fired locked my gun up. When I finally did get the carrier loose the primer fell into the charging handle groove in the receiver.

I really like the 2500-2600 FPS range for my gun but was trying to complete the ladder test.

Any info on that would be much appreciated. If it's true it's definitely something I did not know.
 
Re: Powder: Gas gun vs bolt gun

I called Hodgdon when I heard the same thing. They told be that it does not matter gas vs. bolt. I asked him specifically about the Sierra reloading manual claims about slow powders and higher tube pressures and he said it was all bunk. Told me that they had talked to DPMS and several other manufacturers and they said it is baseless as well. I have since worked up a load using the max charge of Varget (a powder that some say is too slow for the gas guns) and no problems in the DPMS 308. I'm sure there are other opinions out there but the word from Hodgdon is good enough for me. I don't worry about any supposed difference.
 
Re: Powder: Gas gun vs bolt gun

Ok. That's what I was wondering because I was staying inside the recommended charge span and my goal wasn't to develop a max load. It makes me wonder why I had a blown primer then. I talked to another reloading guy and he suggested since it is a new barrel that maybe after I break it in it will possibly clear out any possible burrs in the barrel or whatever caused the over pressurization.

So is there a certain type of powder that is better for gas guns, as in slow, medium, or fast burning?
 
Re: Powder: Gas gun vs bolt gun

Blown primer is a sign of excessive chamber pressure or/and weak brass.

The legends about powder suitability for semiautos (even the notquite gas operated G3/CETME system, sort of a recoil-unlocked, blowback operated setup) are based on port pressure specifications. I know them for the M14 system, which might be the same for the FAL, and I've seen ONE description of the AR15 specs but not for the large-frame .308 and similar versions.

It gets complicated a bit because M14 specs were developed on the CUP system, and QuickLOAD uses piezoelectric PSI standards. AFIK, the .223/5.56mm AR15 spec it piezo PSI, but I'm not sure. A great dearth of online references to that.

Some loads I thought were chamber pressure safe in M14 types but badly overpressure on the port spec (based on pressure modeling for 12.0 inches of bullet travel, about equaling 14.1 inches from the bolt face), actually predict to be on the high side of "safe" for the M14 system once I cross-referenced them with published data on CUP port pressures. I adjusted case capacity, then some small adjustments to burn rate, to match the actual tested velocities at 10 feet (not the military 78 feet for 7.62), and compared the PSI predictions of port pressure with the actual CUP measurements.

Varget and RE-15 are perfectly safe with 175-gr SMKs in an M14 type, up to 2650 fps or so.

The difference is that going over spec with a bolt gun shortens brass life. Doing it in a gas gun gives you excessive bolt speed and all associated extra stresses.

I have not bothered to run the predictions with any powder slower than 4064. Sources are mixed on whether Varget and RE-15 are slower than 4064. I suspect that powders may actually change positions on the ordinal-scale burn rate charts depending on caliber and maybe even bullet weight.
 
Re: Powder: Gas gun vs bolt gun

These are the considerations to make in ammo. Hornady "Light Magnum" says not for use in semi auto's. Hodgdon may test all there loads for semiauto use. M118LR was reduced to use in M14's for the same reason. It was developed for Rem 700 based rifles but too hot for M14's. Gas volume and pressure curves are important for gas operated semiautos.

Speer also lists prefered loads for gas guns.
 
Re: Powder: Gas gun vs bolt gun

I use same load for dpms sass, dpms lr24, fn xp, and savage. No ill effects or problems. Two friends use my loads as well. remmy 5r, and dpms 20 ". 44.5 gr under 175 match king 2.8 ocl. very accurate load. dime covers 5 shot groups. So I am inclined to say from my experience not to worry. But always remember what works for most might not work for all.Just my view from my testing.
 
Re: Powder: Gas gun vs bolt gun

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GGN</div><div class="ubbcode-body">I use same load for dpms sass, dpms lr24, fn xp, and savage. No ill effects or problems. Two friends use my loads as well. remmy 5r, and dpms 20 ". 44.5 gr under 175 match king 2.8 ocl. very accurate load. dime covers 5 shot groups. So I am inclined to say from my experience not to worry. But always remember what works for most might not work for all.Just my view from my testing. </div></div>

Same 44.5 in win brass, 42.5 in LC 178 amax very accurate in sass with varget. 4064 I think was 42.5-43 in win but I don't recall I didn't use it that much.

edit: OP you are loading at max, you need to be careful and start looking for signs of weak primer pockets etc. I did the same thing with mine with 44 grains of AA2520, fed brass and win primers. If I had been using win brass and cci primers I'd have been fine but fed is soft, win primers are a little small and that combination was enough to ruin my range day.

Also, you don't need to load "hot" to get performance out of that rifle I have an 18" one and a 178 amax at 2466 does well out to 500 so unless you are going really far go for an accurate load with a good bullet before you start worrying about getting another 50-60fps. Just my 2cents.
 
Re: Powder: Gas gun vs bolt gun

Powders like 4350 or 4320 and slower have traditionally been on the "no go" list for USGI semiautos in the .30 calibers.

Unlike 6.5 Creedmoor and other calibers more..."exotic" than the ubiquitous .308/7.62 NATO, I just don't see those powders being used all that often...

I've never modeled loads using those powders. Don't have any, might not ever.
 
Re: Powder: Gas gun vs bolt gun

Anyone know if IMR 4895 is ok? I have some of that and if it's ok to use I'll use that. I am fresh out of the 4064 and I've been told 4895 is pretty good stuff.
 
Re: Powder: Gas gun vs bolt gun

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BCP</div><div class="ubbcode-body">4895 is perfect, it's in the middle and works in tons of calibers from 223 to 30-06.

Just be a bit more careful when you load. </div></div>

Oh I will. I didn't think anything of it because I was loading to the manual and I guess I trusted it too much. Had I gotten up and examined each case prior to firing the next one. Lesson learned.
 
Re: Powder: Gas gun vs bolt gun

BCP I agree super great load. My good shooting buddy loved it but read about another load that a guy had won a comp. with. After getting spanked on the range (by me
wink.gif
) he know uses it again and like myself will not use any other load when we use 175's
 
Re: Powder: Gas gun vs bolt gun

Just one little thing I would like to add to this. I don't know if you use all the same brand of brass or not, but military brass is thicker than commercial brass, so there would be higher pressure in the military brass with the same powder charge.
I found a great load using 165gr sierra gameking hpbt over 43gr of reloader 15 for my lr-308 using remington brass. I thought, that I could use that same load in military brass, that I had from shooting some ultramax reman. ammo.
Anyways I noticed that primers were getting pierced in the military brass, so I guess they were too hot. I was very new to reloading then, and I had no idea there was a difference in brass. Lesson learned Hope it helps
 
Re: Powder: Gas gun vs bolt gun

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lukeva</div><div class="ubbcode-body">Just one little thing I would like to add to this. I don't know if you use all the same brand of brass or not, but military brass is thicker than commercial brass, so there would be higher pressure in the military brass with the same powder charge.</div></div>

My early 2000s vintage FC brass is lighter than USGI. The batch of FC I bought last year is virtually identical in water capacity with FA and LC brass.

YMMV
 
Re: Powder: Gas gun vs bolt gun

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RJ Hunter</div><div class="ubbcode-body">+1 H4895 will not hurt anything and most always shoots!! </div></div>


When competing with the M-14, M1A, we always said if it won't shoot with 4895, it won't shoot.
 
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