First cold shot through a suppressor

[sierra one]

Over the last few years I have been concentrating on subsonic rounds through various suppressors in different calibres.

Prior to that all rounds had been supersonic as suppressors are unrestricted here (New Zealand) and I use them on F class rifles in competition and on all my rifles for hunting/ varminting.

I was dismayed to find that once I went below 1200 fps I could not replicate the astonishing groups I had read about when including the first COLD clean shot. This regularly dropped between 4-6" low @ 100 yds of the remaining group. Sure the other 4 rounds would print in 0.5" but pointless for hunting when the bl is cold.

I would dearly love to get to the bottom of this and i am heartened that this is the place to start.

[Murmur]

Hi there,
I couldn't help but ask some questions. I recently purchased a 300/221 TC carbine with suppressor but as I haven't had any experience with reloading since sent my gunsmith for some subsonic load development. He found the rifle to be grouping around MOA for 5 shot groups at 100m. He did however find huge elevation changes with as little as 30-40fps speed deviation. He made the comment that the biggest problem was a cold, clean barrel but in my case the first shot deviation is very close to the main group. He found by very carefully throwing powder charges consistantly the group sizes stayed small & centred.
I could be all wrong as I'm waiting to receive it back for hunting. Barrel harmonics & it seems small case capacitys do strange things. I'll have to post once I get it back & have a little time in the field with it.

[Artful]

Does it do it with Cold dirty barrel? Are you leaving like a coating of oil on your bore? Does it do it without the suppressor installed? Does it do it consistantly the same each time (ie 1st shot down 3 left 1 then the rest back up on point of aim until you clean it again?)

What procedures are you using to clean it?

Was the barrel stress relieved after threading for the can?

[sierra one]

I have experienced it with cold/ clean and cold fouled bls in every calibre I have tested subsonic. The worst and i have to be careful; was a bolt action 300/221 with Sierra 240 gn MKs which was a very expensive disaster. I intend to do another as the case shows a lot of potential but something went wrong with the suppressor design and I suspect the bl profile was too light. I shoot 1000s of rounds on paper and through a chrony but the guys i talk to who hunt rave about them but have no groups to prove it.

The best theory i can offer is the hot gases contained in the suppressor which effect the velocity of the subsequent shot (up to 120 fps difference). I appreciate the loading info but this is with meticulous loading.

If I allow the suppressor/ bl to cool then lovely little groups appear. Can take up to 15 mins though unless I remove and purge the suppressor.

I went to a single shot akin to a T/C so that i could vent the gases quickly and blow though the opened action. This has significantly helped.

Info from the 300 subsonic semi shootes would be of huge interest.

[Murmur]

Hey you might be on to something there about barrel diameter / profile. Now I can't wait to try my TC. It has a short & heavy bull profile full length...I'll let you know once I hit the range.

[Murmur]

Hey Sierra,
Which brand of suppressor did you have the best results with?