crimp pressure

[impalaSS]

I recently posted a question about reloads in a glock in the handgun section. After reading some of the post about to much crimp increasing pressures it got me thinking. Is there any solid information on crimp pressure to pressure rise. Not saying this is a good idea or to try it. But therotically if you increased your crimp enough could you get more powder burn out of a shorter barrel. Like say an 18" 308 barrel you are loosing efficency because of the shorter barrel the bullet is out of the barrel before your powder finishing burning and reaches peak efficenc. So would more crimp hold the bullet in until your powder reaches a higher efficency level? Also could you get the same velocity with less powder and a tighter crimp, as more powder and no crimp in the same rifl?. I dont plan to try any of these theories and would not recomend them to anyone because it would be unsafe. I just found this interesting if there is any data or perhaps some of you know more about this.

 

[Blitzfike]

Internal ballistics is a VERY complex issue. Increasing the crimp can certainly increase pressures. Not very many folks have access to pressure test gear so the next best thing is a chronograph. You can see the results of changes fairly soon in your bullet velocities. I have experimented with changing powders, primers, crimp, bullet lube and a variety of other factors in trying to wring the most out of pistol caliber ammo in carbines. I've found that using slower burning powders with lead bullets lubed with a moly/wax lube can give me 300 fps more velocity than standard loaded jacketed bullets. I started doing this for my son and his Beretta 40 carbine. I have been able to duplicate it for my Hi-point 40 carbine as well. Pressures appear to be in the normal range as measured by case expansion and primer flatness. In order to get the same velocities with more normal powder selections, I see case expansion and primer flattening to a great extent. The powder I ended up using is Accurate #7. Pretty slow for a small capacity case. Bullet seating depth plays a large part is pressures as well. I like Accurate #5 for my more robust pistol loads, but you have to be very careful with is as you can see pressure spikes pretty quickly with bullet setback. (bullets getting pushed further into the case as they are chambered and rechambered in auto pistols.) I tend to use a fairly heavy crimp with #5 to help guard against that. The crimp has much less effect on pressures than the reduced case volumn does. Blitzfike

 

[impalaSS]

Quote from Blitzfike "I've found that using slower burning powders with lead bullets lubed with a moly/wax lube can give me 300 fps more velocity than standard loaded jacketed bullets"

That is a really good idea I have never thought of doing that. I wonder if using a faster burning powder out of a rifle caliber carbine would have the same effect since most rifle cartidriges use slower burning powders.

 

[dennishoddy]

Quote from Blitzfike "I've found that using slower burning powders with lead bullets lubed with a moly/wax lube can give me 300 fps more velocity than standard loaded jacketed bullets"

That is a really good idea I have never thought of doing that. I wonder if using a faster burning powder out of a rifle caliber carbine would have the same effect since most rifle cartidriges use slower burning powders.

In my experience, most powders for long guns are a slower burning, to keep pressure spikes down. Loads that are crimped, etc. can contribute to higher pressures.
Faster burning powders may be useable, but I'd sure back off the max load a lot, and work up, checking for signs of over pressure. Your primer will be the first to tell you what you need to know.

 

[Blitzfike]

Dennis hit the nail on the head as far as rifle powders.. Some rifles are particularly sensitive to powder selection, such as the M1 Garand. Since the gas port is close to the end of the barrel on it, bullet/powder selection is critical with it, to keep the pressure spike within the operating range of the action. Faster burning powders with bullet weights of 168 grains or less or optimal in it. Slower burning powders or heavier bullets can cause the operating rod on a garand to destruct. The key in weapons that aren't sensitive to the pressure curve for gas operation is to choose a powder bullet combination that just finishes burning completely before the bullet leaves the barrel without creating pressures greater than the weapon and bullet can stand. I shoot .204 ruger and .223 Rem out of bolt rifles and have to be careful that I don't drive the bullet so fast that it disintegretes in flight. With a 32 grain bullet out of the 204, I can easily exceed 4000 fps if not careful. Another thing to watch is barrel erosion from the propellant gasses with super high pressure/velocity loads. Many of the early experiments with the .17 caliber chamberings had very short barrel life due to erosion. I've played with using pistol powders in cast bullet rifle loads and while they are cheap to shoot, they leave a lot to be desired in my experience. I prefer to stick with standard rifle propellants with cast bullets and just reduce the charge to keep the bullet velocity at 1200fps or below. Very little leading with gas checked bullets and very accurate. Lots of the things I have tried were things that the so called experts in the magazines claimed couldn't be done. Don't be afraid to try something different, just be sure to research your project to keep it safe. Do a lot of reading and trying established loads before you venture out into the unknown... Blitzfike