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 :uzi2:

[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:confused:

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]

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.

[mstarling]

Do we have any information on the effect of a chamber "upgrade" from 300/221 to 300 BLK on accuracy with sub and supersonic loads yet?

So far there is no real information in this thread.

Thanks!

Mike

[rsilvers]

No you would have to get 10 300-221 barrels, shoot them all with 5 different bullets, 50 shots each, then convert them all, then repeat. A huge and expensive process.

I do have accuracy data for 300 AAC BLACKOUT 16" 1:8 twist with 110 grain Berger and Sierra bullets loaded to 2.1 OAL or less - 0.85 inches at 100 yards for 50 rounds (an average of ten 5-round groups).

[i8asquirrel]

http://img585.imageshack.us/img585/8839/190grspbt10rndgroupz.png (http://img585.imageshack.us/i/190grspbt10rndgroupz.png/)

Uploaded with ImageShack.us (http://imageshack.us)
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!:grin:

[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.

[rsilvers]

No one knows in any sort of reliable way.

[i8asquirrel]

I really dont understand the problem? Its sorta like asking what is more accurate round "A" or round "B".... If you have a good barrel and reload you should be able to make loads for either that are accurate. My Blackout has a little more free bore than My whisper. I think that being a standard cartridge gives the edge to the Blackout! Good luck

[1911man]

No you would have to get 10 300-221 barrels, shoot them all with 5 different bullets, 50 shots each, then convert them all, then repeat. A huge and expensive process.

I do have accuracy data for 300 AAC BLACKOUT 16" 1:8 twist with 110 grain Berger and Sierra bullets loaded to 2.1 OAL or less - 0.85 inches at 100 yards for 50 rounds (an average of ten 5-round groups).

I'd still like to know how you did this????? I can't get consistent groups less than 1.75" with any bullet under 130gr with a OAL in the 2.1" range using 1-8 or 1-10 twist bbls? Rechambered some of the bbls to 7.62x40 WT and they shoot 1" or less so it's hard to blame it on the bore or twist.

Haven't tried any Bergers, which bullet did you use?

[rsilvers]

Berger 110 and Sierra 110 Varminter. This was a test barrel, not an AR15. But it did have the 300 AAC BLACKOUT chamber.

[i8asquirrel]

1911MAN I will try and send you some data this eve. I have multiple loads that are shooting well through both AR and bolt platforms.

[i8asquirrel]

I am loading LC brass,CCI 400 primer for all my loads

#1 125 gr Nosler BT over 18.0 gr 4227

#2 130 gr Speer HP over 20.2 gr 1680

#3 150 gr Speer sp over 15.5 gr H110

Subsonic:
Coal 2.260
190 gr Hornady btsp over 10.5 gr 4227 ( very accurate from my bolt doent cycle great in AR)

220 SMK 908gr 296

Hope this inho helps......

[snipecatcher]

220 SMK 908gr 296



I bet that one has some recoil! :grin:

[i8asquirrel]

SORRY thats 9.8gr ......908 would need I hydralic press for compressed load.
WOW maybe a new wildcat idea?

[1911man]

I am loading LC brass,CCI 400 primer for all my loads

#1 125 gr Nosler BT over 18.0 gr 4227

#2 130 gr Speer HP over 20.2 gr 1680

#3 150 gr Speer sp over 15.5 gr H110

Subsonic:
Coal 2.260
190 gr Hornady btsp over 10.5 gr 4227 ( very accurate from my bolt doent cycle great in AR)

220 SMK 908gr 296

Hope this inho helps......

What is your OAL on load #1 & #2? AR BBl mfg? Twist rate?

[i8asquirrel]

COAL for #1  I think is 2.110" ( what ever the Sierra data had stated for the bullit size)
The Barrel is a Schillen chromolly 1x10" twist 16" long..It was chambered with a PTG .300whisper reamer.

[BWE Firearms]

Is that 220 SMK 908gr 296 load going supersonic or warp speed.:grin:

[1911man]

COAL for #1  I think is 2.110" ( what ever the Sierra data had stated for the bullit size)
The Barrel is a Schillen chromolly 1x10" twist 16" long..It was chambered with a PTG .300whisper reamer.

I thought we were on 300BLK here? I can get Whisper chambers to shoot well too, just not the 300BLK

[i8asquirrel]

1911 they are same = same i think the only differnce on my two is that one is 1x10" and the other is 1x8" :smile:

[1911man]

1911 they are same = same i think the only differnce on my two is that one is 1x10" and the other is 1x8" :smile:

A PT&G Whisper reamer and a 300 Blackout reamer have very different throat lengths, the long throat on the BLK is what makes light bullet (110-125gr) supersonic accuracy harder to achieve.

[rsilvers]

We have seen the opposite - the lighter the bullet, the better our accuracy - at least in short barrels (9 inch). 16 inch has much less of a preference.

[i8asquirrel]

1911 your are cooerct the difference is that the Blackout chamber on my weapon has a looong freebore....:grin: