Oversize bore

dtknowles

The bore on my CZ-52 in 7.62 x 25mm slugged out at .310". I loaded some rounds with .312" dia. gold dots but they won't chamber. I'm going to size some of the bullets down to .311" and see if they will go then. The .308" FMJ's are showing poor accuracy.

Do I try to modify the chamber?

Do I ream the necks on the brass?

Do I buy an new barrel?

Where do I find .309" or .310" bullets?

A thousandth here and a thousandth there and I might get this gun to group.

Tim

Highball

You can cast lead slugs and size them to your hearts content.

nononsense

dtknowles,

These are from Hornady:

https://www.hornady.com/shop/?ps_session=7775a198eebfcd66e20449b3cbb386a5&page=shop/browse&category_id=b30b914a0297302107cd8c4695880db5

Best.

JustC

what do you mean they won't chamber??? is it because the newer bullets when seated in your die are jamming against the lands? if so, seat them deeper and they will chamber. Even the .308 dia pill will jamm against the rifling lands if out too far.

if it won't chamber because the shoulders were bulged during sizing, then the shoulders must be ironed out,...I find throwing them away in this instance is much quicker and less frustrating.

check those possibilities first and let us know what you find out. Simply going up a few thousandths in bullet dia should not cause the non-chambering issue, unless the leade in your CZ chamber is particularly tight compared to other factory chambers, and the ogive is jamming against the leade angle.

Tailgunner1954

The only other think I can think of (JustC covered the rest) is that your firearm has a minimum diameter neck, and with the fatter bullet, your case neck won't fit into the chamber (BTW, this is a unlikely senerio).

Smoke or otherwise color (magic marker) one of your rounds that won't chamber, and try it again. Look for where the round is rubbing (radial marks, lengthwise ones are from the mag rails/feed ramp).

dtknowles

Thanks for the ideas. I have had the barrel in and out of the pistol a half dozen times today. The interfereance is on the lip of the case. Even after trimming the case back to shorter than the trim to length the .312 bullets would not chamber properly. This is just dropping them into the removed barrel. I sized the bullets to .311 and put them in the trimmed cases and they went in far enough that I was willing to test fire them with starting loads. Action closed and locked and the rounds fired as expected for starting loads. Action did not cycle but brass extracted easily when manually cycled. I went ahead and sized the whole box of bullets.

Notes:

The untrimmed once fired S&B cases were .985 inches. The cases that worked are .977 inches. The longer cases work with .308 diameter bullets.

My micrometer said the bore slug grouves were .310 but my dial caliper said they were .311. My micrometer said the sized gold dot bullets were .310 and my caliper said they were .311.

Either way my bullets are now grouve diameter and I hope that they shoot more accurately.

These bullets are .32 ACP 60 gr. Gold Dots and with this starting load they should have been moving at 1200 fps or so. My bullet trap is backed with a number of layers of fiber board. The recovered bullets look awesome. These light slugs cannot do a classic mushroom because they are so short but they did expand almost into a pancake and retained more than 90 percent of their weight.

It will be interesting to see if they can hold together at the 1800 fps that I expect to be able to push them too. My calculator says they would still be traveling at 1100 fps at 100 yards :-) Zero'd at 80 yards it would only be 1 inch high at 50 and less than 2 inches low at 100.

Anyone ever hear of 7.62 x 23. It would be a 9 x 23 Winchester necked down just like the 7.62 x 25 only it would function in 1911 size guns of modern constuction for use at higher pressures.

The real key is that 1911's can be setup to shoot 5 inch or smaller groups at 100 yards.

Tim

JustC

I am still either seeing the shoulders to be pulled slightly fwd by the sizing die, or slightly bulged, try backing the body out a hair, or the chamber is tight. I would measure the thickness of each different make of brass,...the whole thing could hinge on the thicker make of brass being coupled with a now larger dia bullet making the round too large in dia to chamber fully. In that case, thinner brass would fix that situation.

Highball

Calipers are not precision measuring instruments.
As a comparison measurement, they work...but a Micrometer is much better at actually measuring a diameter accurately.

Bear in mind one needs a 1" Standard to check the Micrometer properly...one closes the Mic. and checks to be sure everything is lined up 0'0'...then open to 1" and check with Standard.

dtknowles

JustC

The only brass I am reloading is S&B and it is all from the same box. I have some Chinese Mil Surp but that does not get reloaded.


Highball

My Micrometer's zero is good and factory bullets normally mic at or very close to spec but I don't have a 1" standard to check it against. I used the calipers as a double check, now I am not sure which to believe, I guess I need some more standards. I have some for my scale :-)

If I could outside neck turn the brass, taking off a thousandth or two should not be a problem, Right?? That would reduce the OD by 2 to 4 thousandths and get me back to where they were to start/

I am going to start a new thread to talk about my 9mm problem to avoid the 10 reply lock.

Tim

JustC

they only get locked on here if the info is outright dangerous or ifin somone decides to leave their manners elsewhere before entering a conversation.[;)] Ohh, and the ones by the azzhats that seem to think this is a good place to start some topic reminiscent of the ramblings of the bi-polar population once they decide they don't need their meds.[:D]