Author Topic: Barrel length's effect on Pressure (Read 377 times)

koli · « **on:** October 23, 2005, 02:58:38 PM »

Does Barrel length have an effect on pressure? Say a 22 inch vs 24 in barrel on a rifle.

Graybeard · « **Reply #1 on:** October 23, 2005, 06:28:11 PM »

Uh, well yes and no.

There is a very definite difference between those two barrel lengths 23" from the bolt face. But up until that point nope none at all. From firing pin strike until bullet gets to the end of that 22" barrel both would be the same ALL OTHER THINGS BEING EQUAL which of course they never are.

Castaway · « **Reply #2 on:** October 24, 2005, 01:31:17 AM »

I'm not sure if I understand your question. As far a pressure goes, it peaks within inches of the chamber. Like GB said, all things being equal, but... a longer barrel will contain that pressure longer resulting in move velocity, but the peak pressure of the load doesn't change.

koli · « **Reply #3 on:** October 24, 2005, 01:59:06 AM »

Thanks guys. That answered my question.

I have not started reloading yet. I am in the "read everything I can get my hands on" phase. I noticed that some "recipies" state the gun and barrel length. I do understand that longer barrel length increased velocity but wondered if and how it effected pressure. Thanks again and don't be surprised if you see more questions from me.

ps. guess I should have included the above information in my original post.

Questor · « **Reply #4 on:** October 24, 2005, 06:15:38 AM »

Follow the recipes in the manuals exactly and you'll be OK. Any of the commonly documented signs of excessive pressure are unreliable in that pressures may far exceed the SAAMI specification before those signs appear.

There are more variables than barrel length involved in determining the actual pressure. Bore diameter has a big influence.

Iowegan · « **Reply #5 on:** October 24, 2005, 06:53:48 AM »

Though bore diameter and chamber dimensions do affect chamber pressure, they are "fixed" in your gun and you really can't do anything about them. The single biggest issue with chamber pressure that you can control is bullet seating depth. A bullet seated just a few thousandths too deep will increase chamber pressure dramatically. Follow the powder charge weight and COL listed in your reloading manual. Don't substitute bullets for other brands or styles. Example: a 160gr 7mm Speer Mag-Tip is .065" shorter than a 160gr 7mm Speer Boat Tail Spitzer. If you used the same COL for both, the BT Sptz will seat .065" deeper in the case. That will increase chamber pressure by several thousand psi. A different brand or bullet weight could make even more pressure and could be very dangerous.