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?

[Mike Bell]

im not positive but I thought some guys on here were test shooting the 300blk ammo in the .300/221 chambers with no problems. I have a tp555 300/221 barrel and Im going to try the 300blk reloading dies. and see what happens

[rsilvers]

Some 300-221 dies are in spec for 300 AAC BLACKOUT. That does not mean the chambers are the same. Shooting 300 AAC BLACKOUT ammo in a 300-221 chamber would be like shooting 5.56mm ammo in a 223 chamber - higher than normal pressure will result.

[Mike Bell]

Is the longer throat on the BLK the only difference? Im not to sure

I was thinking that as long as Im not shooting the 240 or bigger bullets that I will be ok. Because the bullet would not be jammed into the rifling (or fit in my mags)


I have a Tp555 barrel in 300/221 also. But I was going to buy the Forster 300BLK dies....Am I on the wrong path?

[rsilvers]

Originally Posted by Mike Bell

I was thinking that as long as Im not shooting the 240 or bigger bullets that I will be ok. Because the bullet would not be jammed into the rifling (or fit in my mags)

You can be fine with handloads if you load them as if they were 300 Whisper(R). But 300 AAC BLACKOUT full power ammo will have higher than SAAMI pressure in your barrel even if the bullet does not touch the lands.

5.56mm ammo does not touch the lands in a 223 chamber, but it will have excessive pressure also.