Interesting Sizing Comparison

[#40Fan]

A fellow member, Mustang, graciously sent me some GC'd and PC'd bullets in .308 in varying sizes from .308 to .311 and today I finally got out to shoot them. These were shot in my 300 BLK with 10.5" barrel at 50 yards and I have been having a rough time getting any of my cast bullets to shoot with any accuracy.

Here are the results from shooting 5 shots of each of the four sizes with everything being the same but the bullet sizing.



I find it interesting to see that the .308 sized bullets shot the best group of the four. I have finally slugged my barrel and it measured .308, as expected. I have a .308 sizing die that is supposed to be here today. I will size the remaining GC'd bullets that I have left over down to .308 and shoot again to make sure it wasn't a fluke. I also found another powder that gave me great results with my cast and PC'd bullets that I plan to use with some of these GC'd bullets as well as the powder I used with them today.

Just about when I was ready to give up on these casts.

Another huge thanks to Mustang.

[Rcmaveric]

Have you made a chamber cast yet? Use the biggest bullet that will fill the throat and chamber. If you slugged @ .308 then the .310 is more appropriate. However if the .311 chambered and shot then it would have a higher accuracy potential. Try loading up about 10-15 more with the .311 and see if the flyer+ stringing is you or the load. I don't know if you are using scope or iron's but its is way to easy to roll your hand while pulling the trigger. Also you didn't say if you were going sub sonic or sonic, when going sub you can have wide velocity spreads due to small charges. Different bullet diameters is going to change your internal ballistics which will affect harmonics and burn characteristics and pressures. A small load tune may be needed with new bullet diameter. Also I recommend shooting over a Chrono, if you see vertical groups and you see wide velocity changes its a dead give away what happened (not consistent case charge or not consistent powder ignition. With those .309's also giving flyers. Maybe a poor accuracy node. Lots to play with here. Bright side is since they are PC'ed you cant blame lube purging.

[lightman]

That is interesting but not really surprising. Thanks for the picture of the group, I like the color and numbers on the target.

[Bent Ramrod]

I found to my surprise that my Shilen-barreled .30-40 Krag rifle preferred cast lubricated boolits sized to 0.308” above the other usual diameters. No leading in the barrel or evidence of blowby in the throat.

Every gun is a law unto itself. Not to say the more usual diameters were not accurate, but off the bench I got slightly tighter grouping at 100 yards and noticeably more hits at long distances from the 0.308” size.

[#40Fan]

With everything I have read on the internet, I don't think I have ever seen a suggestion to try the actual bore size when using casts. When Mustang said he had that size available, I jumped on the offer. Now I have my own .308 sizing die, so I can run even more tests.

Rcmaveric, when I said I slugged my bore, I meant I did a chamber cast. I now realize there is a difference. The inch of bore in front of the chamber measured .308". I am shooting subsonic loads with a scope and I normally would have chrono numbers, but with the off chance of a GC coming off, I wasn't going to risk a possible strike. My shooting is fine as I can put 5 shots next to each other with jacketed bullets.

[plainsman456]

I would try some more of those sized 308.

See if it holds up over the long run.
You can always go larger if needed.

[Love Life]

I found this to be the case when accuracy testing a 308 Winchester. Smaller shot better. I got best accuracy at .309. Proved it out by shooting over 200 rds each of .311, .310, and .309 to distances up to 300 yards.

I quit there and bought a bunch of 175gr Sierra Match Kings, lol.


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[HangFireW8]

If you haven't heard on the Internet, or this board, to try sizing to bore diameter, then you are not paying attention. I've pointed out repeatedly that throat sizing is NOT always the only path to accuracy.

What is going on here beggars the imagination. This guy shoots tighter groups with bore sized boolits and the first post reprimands him to tow the line and do a throat cast and size larger.

Can anyone say echo chamber?

[Love Life]

I started sizing smaller as I thought squishing a bullet that much into a tube was detrimental.


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[jmort]

Glen Fryxell sizes his .357 mag bullets at .357, at least that is what one of his articles says. What the OP did makes sense, check it out.

[codgerville@zianet.com]

If you haven't heard on the Internet, or this board, to try sizing to bore diameter, then you are not paying attention. I've pointed out repeatedly that throat sizing is NOT always the only path to accuracy.

What is going on here beggars the imagination. This guy shoots tighter groups with bore sized boolits and the first post reprimands him to tow the line and do a throat cast and size larger.

Can anyone say echo chamber?

Agree. I have two 30-30 rifles, a Stevens 325, and a Marlin 336. Both are .3085 groove diameter. I only shoot 311041 sized to .309 with excellent accuracy and no leading. Have thought about making a .3085 sizing die, but what I'm using works fine. If it ain't broke don't mess with it.

[HangFireW8]

A little history. In 1957-58 Col. E. H. Harrison of the NRA published his cast bullet research in the American Rifleman. In part 4 he covers important accuracy concepts like a section on "Delivering bullet straight into barrel." If this is accomplished by any means, the chances of developing an accurate load are very high.

With commercial 308Win rifle throats (meaning: not quasi-military, or actual military 7.62NATO throats), there just isn't much jump until the boolit engages both the rifling and the bore. So sizing to bore or bore + .001" is sufficient for a concentric boolit start.

As with any loading for accuracy, excessive sizing (such as .314"+ down to .308") will increase boolit eccentricity, which will decrease accuracy. So if anyone cares for an intelligent discussion, it's not just the size of the boolit and the throat. It's the concentricity of the boolit, the concentricity of the cartridge case, the consistency of release and the concentricity of boolit engagement into the leade.

In other words, one person shooting boolits cast at .309", sizing and shooting them at .309" will probably get better results than someone casting them at .314" and sizing them down to .309".

If everyone here would just read these 4 articles, a lot of the posturing and claims here would just go away. Well, maybe. You see, back then the articles were published with a targeted reading audience of men having a high school education, and assuming employment in some kind of job requiring mechanical ability, or the desire to learn such. Nowadays the reading level would be Sophomore in college, and assumed mechanical ability would be something well beyond "mimic what I do in a youtube video".

I'm not against sizing for the throat. But it is just not always necessary, sometimes harmful to accuracy, and occasionally impossible.

[Rcmaveric]

I am all about learning new tricks. I have read other articles that talk about sizing bullets affecting accuracy due concentricity. I am searching for the article mentioned by HangFire now. Minimum sizing has worked well for me in a number of riffles and sizing to throat is the minimum, and its only a couple thousands larger. Oddly enough as #40fan used less sized bullets his groups worsened. He can very well purse that .308 sized avenue and tune a load for that size bullet with success. If he can and then report back I would love to see his results. I recommended a chamber cast to him to see what the inside of chamber looked like so he could match a bullet better, gain a little insight into what is happening in there. We all have our own opinions about what works for us. I don't think anyone is wrong. Most often it is about our own experiences and knowledge base. I have read of using grooved sized bullets, just never tried it due to lack of need. If I bore size a bullet I normally paper patch it afterwards.

Jmort- Not sure about Glen Fryxel reasoning but Todd Spotti and his friend Rick at LASC in Mr. Spotti's article "Questing For The Perfect Cast Bullet Load For The Freedom Arms 357." said he sized to .357 for a .357 Mag because that is what fit his chambers and the only reason larger bullets were used is because they would rattle around in the cylinder chambers. In his case a .358 bullet wouldn't fit.

[RED333]

Am I off base to think neck tension comes into play?

[MUSTANG]

In this specific case; I believe that posts #12 and #13 may have drawn incorrect conclusions. The RCBS 165Sil boolits provided were as follows:

All were cast from 96% Lead, 3% Antinony, and 1% Tin.
As cast they were air cooled, and tested at 9.8 BHN using a Lee Hardness Tester.

Cast to ~ .310 on drive bands (one side .309 as cast - rotate 90 degrees and the measured .310 - slight oval on bands).
Aluminum Gas Check (Amerimax .014 thick) placed on each boolit by positioning base of boolit shank on gas check and tapping nose lightly with a plastic faced hammer - ensuring boolit sits squarely on shank.
Sizing boolit and gas check in .308 in Lee push through sizer.
Powder Coated with HF Red & Baked at 400 degrees for 20 minutes. (Measured .311 after Powder Coat).
Sized 1st group at .311 in Lee push through sizer.
Sized 2nd group at .310 in Lee push through sizer.
Sized 3rd group at .309 in Lee push through sizer.
Sized 4th group at .308 in Lee push through sizer.

In #40Fan's testing, those sized the most; shot the best groups in his rifle and load.

The RCBS 165 Sil Nose rider boolit, and a sized diameter of .308 and .309 seems to work best in his sampling test.

[HangFireW8]

I never said more-resized boolits always shoot worse. I was just pointing out that sizing boolits introduces the possibility of more eccentricity, which is a negative factor for accuracy. Most here can never notice it because a.) It is a factor they do not control for (test), and b.) they are shooting over 1MOA groups on average. Just another factor to consider, that sometimes gets ignored in these forum discussions.

Another factor that gets ignored is case runout. I was dumbfounded that one of Goodsteel's free custom rifle recipients (I'm not talking about Larry) didn't even measure, or know about, how to measure and control this factor. When I pointed it out I was met with arguments of doesn't matter, I load accurate ammo, etc., etc., which just means these people cannot shoot consistent 10 shot groups under 1MOA due to fliers, don't know why, but they sure do have a good wallet group or two of 5 shot groups.

Am I off base to think neck tension comes into play?

As for neck tension, the two keys are a.) consistency and b.) not marring or deforming the boolit with excessive crimp. In the articles, one conclusion is that neck tension doesn't matter. That doesn't mean you can crimp the heck out of it, nor does it mean you can have a batch of ammo with bullet pull varying from 1 to 60 pounds. It means if you load properly, you can select any reasonable bullet pull, do it consistently, and find accuracy. This general statement was about rifle and medium burn rate powders. Of course there is H110 and magnum revolver loads, but that is a different topic from bottleneck high power rifle accuracy. Also a tight case neck that resizes the boolit on seating can be a negative as well.

[243winxb]

Going to base results on 5 shots each? Really.

. I will size the remaining GC'd bullets that I have left over down to .308 and shoot again to make sure it wasn't a fluke.

Great idea. Awaiting results.

Sizing down more then .003" may hurt accuracy.

[HangFireW8]

Going to base results on 5 shots each? Really.



Great idea. Awaiting results.

Sizing down more then .003" may hurt accuracy.

Good idea to retry, and try more shots per group (I kind of hinted at that above when I mentioned 10 shot groups), but the OP is using Powder Coated boolits obtained from another forum member... I don't do PC but I don't think post-coating sizing works well. Given all that I don't think a quick retry is in the offing.

As a side topic, I still do load ladders in 5 shot increments, but after that most of my shooting is done in 10-shot groups (or sometimes, "as many as I got" groups where "got" > 5).

[Andy_P]

An interesting start to what might be an informed challenge to some long-standing dogma about the "correct" size for best performance.

I challenge the suggestion that "eccentricity" is as important as stated. I made up some cast bullets and severely deformed the nose portion using side-cutters and a belt sander, and their accuracy seemed undiminished at 100 and 200 yds. Not scientific, but others have seen the same, so long as the base of the bullet is not deformed.

[james nicholson]

Thanks for the test and your info #40Fan, at least you tested something instead of reading about something before making comments. You are on the right track, test it, record it, do it. In your rifle you have a good start but more testing is in order, 5 rounds is the starting point.