Impact of chamber "upgrade" on accuracy?

[mstarling]

Guys,

Anyone have real data on the impact of upgrading a 300/221 chamber on one of tp555's barrels to the 300 BLK (both sub and supersonic)?

Very interested in the effect of doing so.

Thank you!

Mike

[tp555]

Haven't done many at all.I'd like to hear this also. Translation: the clymer 30/221 based chamber is tighter and has a shorter throat distance.The 300aac blackout has some room for the case and longer throat.So how do the old loads work in the new chamber with longer throat.Do you have to change the bullet seating closer in the new chamber?

[1911man]

From what I've seen so far it's negative, my test bbls chambered in 300/221 shoot better than 300AAC chambered ones, mfg and bore spec the samel

As a reference "match" chambers in .223 and .308 both have tighter throat diameter and shorter freebore than std SAAMI spec.

Also there are advantages from loading shorter, especially with 110-135gr supersonic loads such as: fits/functions in unmodified AR mags and full bullet/case neck contact aids in accuracy when fed from a semi-auto

Have test bbls coming in with .3085" diameter throat and throat length optimized for 2.00-2.100" OAL ammo, we'll see??????

[mstarling]

Have been very pleased with the accuracy of my tp555 barrel with 125 gr NBTs ... would hate to have that open up to more than an MOA.

Guess I'll wait to hear more abt the accuracy of the 300 BLK

Mike

[snipecatcher]

I've got one of TP555's barrels on order right now in 300 BLK. Every rifle is different of course, but I'll share my observations when I start testing loads.
-Dan

[mstarling]

Any new information out there?

[i8asquirrel]

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I have a boltgun chambered in .300 Blackout with a PTG reamer. It is the most accurate 30 cal I have ever owned. the rifle barrel is a schillin blank thats was 1x8" wtist that is 16" long. Its dedicated to subsonics, the picture is a group of 11rounds total fired at 100yds. I had a called flier so I fired 11 instead of 10 rounds so the group would be 10 total. as best I can tell its .122" CTC .......
If your thinking of chambering to .300 blackout, do it! you wont be sorry.

[rsilvers]

With our 50 round test all shots were included in the 0.85 group at 100. No doubt one can find some really small 3 shot groups in there.

[i8asquirrel]

Well I think that the cartridge lends itself to being accurate due to the light recoil and High BC. of most the bullits used. I feel that this round aside from having many tactical uses is going to be a great round for up and comming shooters ( my Grandkids). I want to have a centerfire round for them that is deer capable but light recoilling...300 aac blk fills the bill nicely!

[mstarling]

I agree that any of the 300 Whisper, 300/221, 300 BLK cartridges will fit the bill for the young shooter.

The question I posted was really aimed at the question ... "What price would I pay in accuracy for having my upper rechambered from 300/221 to 300 BLK?"

Must admit that is the cost for supersonic accuracy is too great, I would be hesitant to have the barrel rechambered.