Best 45ACP Suppressor barrel length for a rifle

Keepin_Jeepin · October 16, 2018, 05:13 AM

So I have a 45 can on the way, should be approved this month or next. The reason I went with .45 because its typically inherently subsonic. I want to make the quietest rifle possible. Platform will be a T/C G2 contender single shot for obvious reasons. The suppressor is a YHM Sidewinder 45

I am afraid of loads working up supersonic speeds at greater barrel length. Judging by various sources including ballistics by the inch with standard pressure loads that should not be much of an issue, and I can load my own if necessary. Id prefer to buy standard velocity stuff from the store that is going to stay subsonic because I dont have much brass right now in 45.

What I am really interested in though is chamber pressure, because that is a factor of noise as well. 45ACP is a low pressure round to begin with but there is a point where pressure will drop exponentially.

My question is where is that? I cant find any pressure data per inch of barrel for this round. From a 16" barrel to an 18 or 20 would it be worth the hassle going the extra length for exponentially less chamber pressure to make it noticeably less quiet? At 18 or 20 inches would standard pressure rounds be supersonic by then? I dont think they are at 18 but I dont know about 20 and beyond.

Basically how long of a barrel can I get before the law of diminishing returns?

Mobuck · October 16, 2018, 06:29 AM

I'm not at all sure you can break 1100fps with any bullet weight (over 200 grains)from any length barrel using the 45ACP case at normal pressures. Barrel lengths much over 12" are going to begin to slow down as the gas expands in such a big bore and pressure drops.
Next question is what purpose could possibly be met by a single shot rifle length barrel with suppressor in 45ACP(other than personal satisfaction)?

Screwball · October 16, 2018, 07:03 AM

http://ballisticsbytheinch.com/45auto.html

http://ballisticsbytheinch.com/45auto2.html

Personally, I’d keep it at 16” for maneuverability, especially with a can at the end. But I agree... definitely nothing to gain going longer with common .45 ammo (230 grain).

I probably will thread my 16” Macon Armory D/I .45 upper when I move out of NJ, but don’t really think I’ll go through the hassle of shortening it.

Keepin_Jeepin · October 16, 2018, 02:08 PM

Quote:

I'm not at all sure you can break 1100fps with any bullet weight (over 200 grains)from any length barrel using the 45ACP case at normal pressures. Barrel lengths much over 12" are going to begin to slow down as the gas expands in such a big bore and pressure drops.
Next question is what purpose could possibly be met by a single shot rifle length barrel with suppressor in 45ACP(other than personal satisfaction)?

Well thats good news.

Its just a fun rifle. Making the best use of a suppressor being a single shot. Ive also built a Mac rifle just for fun, and have a 1911 for this can. Just wanted a platform to use the suppressor as efficiently as possible.

smee78 · October 16, 2018, 05:41 PM

I had my 1911 Mec tec threaded and it makes a fun host, I liked it so much I went ahead and built a Palmetto State PA-45 pistol to also have fun with. I have found my favorite host pistol to be my FNX-45. Good luck with you new toy.

Mobuck · October 17, 2018, 05:58 AM

Guess if you're going to call it a rifle, you're stuck with 16".

October 16, 2018, 05:13 AM	#1
Keepin_Jeepin Senior Member Join Date: October 3, 2007 Location: Chelan Posts: 161	Best 45ACP Suppressor barrel length for a rifle So I have a 45 can on the way, should be approved this month or next. The reason I went with .45 because its typically inherently subsonic. I want to make the quietest rifle possible. Platform will be a T/C G2 contender single shot for obvious reasons. The suppressor is a YHM Sidewinder 45 I am afraid of loads working up supersonic speeds at greater barrel length. Judging by various sources including ballistics by the inch with standard pressure loads that should not be much of an issue, and I can load my own if necessary. Id prefer to buy standard velocity stuff from the store that is going to stay subsonic because I dont have much brass right now in 45. What I am really interested in though is chamber pressure, because that is a factor of noise as well. 45ACP is a low pressure round to begin with but there is a point where pressure will drop exponentially. My question is where is that? I cant find any pressure data per inch of barrel for this round. From a 16" barrel to an 18 or 20 would it be worth the hassle going the extra length for exponentially less chamber pressure to make it noticeably less quiet? At 18 or 20 inches would standard pressure rounds be supersonic by then? I dont think they are at 18 but I dont know about 20 and beyond. Basically how long of a barrel can I get before the law of diminishing returns?

October 16, 2018, 05:41 PM	#5
smee78 Senior Member Join Date: July 14, 2008 Location: South Carolina Posts: 2,918	I had my 1911 Mec tec threaded and it makes a fun host, I liked it so much I went ahead and built a Palmetto State PA-45 pistol to also have fun with. I have found my favorite host pistol to be my FNX-45. Good luck with you new toy. __________________ We know exactly where one cow with Mad-cow-disease is located, among the millions and millions of cows in America, but we haven't got a clue where thousands of illegal immigrants and terrorists are

October 16, 2018, 06:29 AM	#2
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	I'm not at all sure you can break 1100fps with any bullet weight (over 200 grains)from any length barrel using the 45ACP case at normal pressures. Barrel lengths much over 12" are going to begin to slow down as the gas expands in such a big bore and pressure drops. Next question is what purpose could possibly be met by a single shot rifle length barrel with suppressor in 45ACP(other than personal satisfaction)?

October 16, 2018, 07:03 AM	#3
Screwball Senior Member Join Date: May 16, 2012 Location: ME Posts: 771	http://ballisticsbytheinch.com/45auto.html http://ballisticsbytheinch.com/45auto2.html Personally, I’d keep it at 16” for maneuverability, especially with a can at the end. But I agree... definitely nothing to gain going longer with common .45 ammo (230 grain). I probably will thread my 16” Macon Armory D/I .45 upper when I move out of NJ, but don’t really think I’ll go through the hassle of shortening it.

October 17, 2018, 05:58 AM	#6
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	Guess if you're going to call it a rifle, you're stuck with 16".