Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
Member Login

Site Notices
Posted: 3/10/2013 6:18:52 PM EDT
My 4.5" tacsol upper for my 22/45 keeps all ammo subsonic but my 4.25" barrel on my cmmg upper seems to have almost a 1/3 of bulk pack ammo go supersonic.
Link Posted: 3/10/2013 6:31:30 PM EDT
Smaller diameter bore causing more powder to be burned?
Link Posted: 3/10/2013 6:46:26 PM EDT
Fast burning powder that burns all the way before exiting the longer barrel. Peak velocity is reached inside the longer barrel and the additional length only serves to slow the bullet down through friction. This is the same reason that carbines chambered in pistol calibers tend to have lower muzzle velocity with longer barrels.
Link Posted: 3/10/2013 6:49:10 PM EDT
Originally Posted By xXNuggettXx:
Fast burning powder that burns all the way before exiting the longer barrel. Peak velocity is reached inside the longer barrel and the additional length only serves to slow the bullet down through friction. This is the same reason that carbines chambered in pistol calibers tend to have lower muzzle velocity with longer barrels.


Someone didn't read the actual question...
Link Posted: 3/10/2013 6:50:59 PM EDT
Bolt weight, bore diameter and bore condition are the big players.
A heavier bolt will increase velocity on blowback firearms.

And is your 4.5" really a 4.5" or is it closer to 5" when you include the chamber adapter and barrel threads and such?
Link Posted: 3/10/2013 6:57:21 PM EDT
It's a deidicated upper that has a .22lr barrel with collar. Threads and all it is 4.25". I'm not sure there is anything else that adds length but I guess I could be wrong.
Link Posted: 3/11/2013 6:39:22 PM EDT
measure from the breech to the end. I think there's like an extra 1.5 inchs of barrel in the upper receiver ot ar15 22 uppers. Rember those m4 uppers? 14.5 inches showing but they had an extra inch and a half inside the upper making them legal. That's weird, you would think the ruger bolt would be heavier.
Link Posted: 3/11/2013 7:02:30 PM EDT
[Last Edit: 3/11/2013 7:35:46 PM EDT by ds3_09]
Originally Posted By dino1:
measure from the breech to the end. I think there's like an extra 1.5 inchs of barrel in the upper receiver ot ar15 22 uppers. Rember those m4 uppers? 14.5 inches showing but they had an extra inch and a half inside the upper making them legal. That's weird, you would think the ruger bolt would be heavier.


I measure by sticking a cleaning rod in to be flush with the breach and marked it at the muzzle. The section of cleaning rod was 4.25". I am definateky having some rounds go supersonic according to my chronograph. I don't understand how really.
Link Posted: 3/12/2013 12:31:38 AM EDT
Could also be a tighter/rougher chamber causing ejection to be a bit later.
Link Posted: 3/15/2013 7:02:58 PM EDT
Strangest thing. I shot 100rds through it today and I didn't hear a single sonic crack. I don't know if the spring has worn in more causing it to have slightly less velocity or the warmer weather just affecting what velocity is subsonic.
Link Posted: 3/19/2013 7:32:18 PM EDT
[Last Edit: 3/19/2013 7:32:42 PM EDT by RDTCU]
Originally Posted By ds3_09:
Strangest thing. I shot 100rds through it today and I didn't hear a single sonic crack. I don't know if the spring has worn in more causing it to have slightly less velocity or the warmer weather just affecting what velocity is subsonic.


Could be. The speed of sound is lower at colder temps, so if you're just at that threshold, the warmer weather could put you at subsonic.

Here's you rough calculator:
http://www.sengpielaudio.com/calculator-speedsound.htm
Link Posted: 3/19/2013 7:46:54 PM EDT
All other things equal I will go with bolt velocity.
Top Top