Choosing Correct Sizer...

[Naga]

I just slugged the bore of my M39, and it came out to .3112" in the grooves. Since I will be using a Lyman 314299 mold, I will need to use a bullet sizer. I planned on ordering one of the Lee sizers, since it works without needing an additional lubri-sizer. Before I order it, though, I would like to confirm: Would .312" be the correct sizer to order?

Thanks.

[RU shooter]

I would go with .314

[krag35]

I would go with .314

+1 .314 has always worked best for me in the Nagants I have owned

[Bret4207]

You probably won't need to size at all. You will find the sizer makes applying gas checks much easier though.

[Naga]

Thanks for the replies. I always thought that boolits were supposed to be sized .001" over groove diameter. .314 would be .0028 over. This will not cause any problems or anything?

[Kskybroom]

+ .314 Works for me too ...

[excess650]

Thanks for the replies. I always thought that boolits were supposed to be sized .001" over groove diameter. .314 would be .0028 over. This will not cause any problems or anything?

Your thought of .001" over groove would be a good choice if your rifle doesn't have an oversize throat. What is the inside diameter of your fired case necks? What is the diameter of the throat ahead of the chamber?

Having your barrel do the .0028" sizing won't be a problem.

[Bret4207]

What Excess said/ You want +.001 MINIMUM in most guns. There are rare guns that like certain loads with certain designs with certain alloys, etc, at just groove diameter or half a thou over. But most surplus rifles will eat +.002-3 with more joy than +.001. An very smooth barrel with a tight neck/throat area would be more likely to benefit from the +.001. Most surplus rifles don't have those qualities.

You also won't be pushing your cast loads very hard to start with if you are smart. Low and slow to start, record your observations, change one thing at a time and slowly work up.

[phaessler]

I concur on the " + 0.002-3 " , every older rifle I have sans a Nagant seems to digest them easier.

Great advice Bret4207...
Pete

[truckjohn]

Lucky you - sounds like you got a good one... I bet it's a really fine shooter! Those Finn's have a good reputation.

Did you slug all the way through or just do a throat slug? If you slugged all the way through - do another but only slug the throat... That's where it matters the most.

The usual advice for "Com Block" pattern weapons is to use whatever fits into a fire formed case (And/or reloading die).... because it's the chamber neck and/or the bullet seating die that limits boolit choice in these... usually... Your Finn may be an exception here... but check it out. The last Mosin I sold off needed a 0.314" slug - but my die wouldn't let me run one bigger than 0.312".... Then, I rigged it up and seated one and it wouldn't chamber.... *Sigh*

Thanks

[Naga]

Thanks for the advice, everyone. How do I go about doing a throat slug? I have only read about slugging the whole bore. How far down the throat do I push the slug? Again, thanks.

[Naga]

Sorry to bump this thread, but since this message pertains to the topic, I decided against posting a new topic.

I finally got out to the range with the M39. I figured out why the guy was selling it for such a low price, given the condition of its rifling: It wouldn't cycle! Luckily, though, this wasn't my first Mosin, so I had an idea: Ten minutes later, after tweaking the interruptor with a set of needle nose pliers, the gun worked like a charm.

I shot Prvi Partizan, both the lighter SP kind, as well as the heavier FMJ kind. Unfortunately, I failed to keep track of which ammo I used for which shots. However, at 25 yards, I managed to shoot a cloverleaf. At 50 yards, my grouping was a vertical string about an inch wide and two inches tall. At 100 yards my astigmatism started to work against me, and I only managed about a 3.5" group.

It might not sound too good, but given my rather meager shooting skills and astigmatism, as well as my lack of a proper set of bags to shoot from, I would say that the vertical stringing at 50 yards and the large grouping at 100 yards were my fault.

I measured a spent casing, as well as figured out how to do a throat slug, and I got some interesting readings.

The outer diameter of my case neck is .3376", according to my Lyman micrometer. The inner diameter of the case neck is .3150" according to my cheap hardware store caliper. However, when I slugged my throat (using a filled casing, and hammering a lead sinker into it until the hammer started to bounce upon impact,) I got .3113".

This doesn't seem to make any sense to me, since I assumed the throat should be significantly larger (relatively speaking) than the rest of the rifling. I double checked this measurement, and it came out the same.

Could I be measuring this wrong, or could I have just lucked out with this rifle? Either way, now that we know the dimensions, does anyone have any advice? Thanks.

[BABore]

It takes some practice to make a good throat slug. Seat a 0.314 boolit backwards and see if it fits the throat and measure where the 0.314 diameter stops from the case mouth. If you seat one of your 0.314 boolits normally, will it chamber with just a little resistance?

[Dutch4122]

One thing to watch for that I have noticed when measuring the inside of a case neck from a casing fired in the rifle. The inside measurement of the case neck may be dependant on case brand. I have found that Remington case necks are usually a bit thicker; and give a smaller inside diameter measurement. Winchester and Privi cases are usually thinner; and will yield a larger inside diameter case neck. For example, I use Privi brass in all of my 7.62x54r loads and I can tell you that out of 5 Mosins (M-39, M91-59, Pre war and wartime 91/30's, 1917 Remington M91) they all measure .318" inside the case neck after firing with Privi brass. I have several molds that drop .318" or larger and so I size my boolits to .317"

The oversize boolits swage down and I have had no pressure issues in any of my rifles; as well as no leading.

I have only bore slugged one of these rifles, the 91/59 carbine, and the bore slugged .315" which is what got me to initially try a .317" slug.

Hope this helps,

[madsenshooter]

Good observations Dutch, some of the little things like that slide right by most folks! I got lucky and scored a .311 sizer off ebay that sizes to .3115, looks like someone's homemade die. With Remington brass in my Krags, that leaves about .0005 for neck expansion, they've been shooting great and chambering the rounds is no problem.

[rhbrink]

Naga, I would guess that you are pretty close on the dimensions. My '39 case neck outside measures .338 I can slide a .316 boolit in the case a wee bit tight but it will fit. The throat just ahead of the case measures .313, out by where the rifling starts it measures .311 with a very long gentle lead going into the rifling. The throat is quite long I don't remember the measurement but I can seat a boolit way out. I have been sizing the boolit down to .314 and it shoots very well. Some boolits with a long bearing surface I have inverted the boolit and pushed the nose first down into a .310 die to size the front band down for a better fit. Seems like a lot of sizing but they shoot very well.

[Dutch4122]

Good observations Dutch, some of the little things like that slide right by most folks! I got lucky and scored a .311 sizer off ebay that sizes to .3115, looks like someone's homemade die. With Remington brass in my Krags, that leaves about .0005 for neck expansion, they've been shooting great and chambering the rounds is no problem.

Thanks madsenshooter:mrgreen:

This method seems to really work well with a bore rider that nose engraves on chambering. The rear end of the slug only has .001" clearance as it leaves the casing; and the nose end is engraved, so both ends are a nice snug fit. The only direction the boolit can go is straight into the bore.:2_high5: