Slugged my Microgroove 30-30

[Wendyj]

I have never done this before but size seems off. I ran some rem oil through the bore of clean rifle. Lubed an egg sinker with Lee brass lube. Tapped it in and used a plastic punch until about 1 inch in the bore. I used a rod and pushed the bullet through with no issues by hand. I can see rifling all over the lead but it measured out low end at .300 and high end .305.5

Isn't that undersized for a 308 bore? I am trying to find out why it won't shoot the 165 grain Missouri white tail bullets I bought less than shotgun patterns. Bullet is lubed no gas checks and sized at .311. Not having much luck with loading for this rifle. Have also loaded up jacketed Sierra SP with IMR 3031 powder and groups are worse. I finally found a box of Remington 170 cor locs to try through it next range trip but not expecting much better. I would rather load my own. Is the sizing off? I ran two through since I was getting the erratic readings. I thought cast was to be .01 or .02 over slugged size.

 

[Chainsaw.]

I am by no means an expert on the subject of either slugging bores or micro groove barrels so Ill just say this, I THOUGH I had heard that they do tend to run tight.

On your accuracy issues, have you tinkered with the cartridge over all length, i.e. how far into the case you are seating the bullet? Also did you find a velocity node that works?

 

[FrankenMauser]

I wouldn't feel confident about those dimensions.
It should be closer to .306/.308.

My suggestion:
Make sure the calipers are zeroed and you're not skewing the reading with excessive pressure or sloppy jaws.
Try a different lube and slug again. My choice would be a very light coat of axle grease (non-moly); or a light coating of a light oil (just an oiled patch through the bore a few times).


According to legend, and some of my own experience, Marlin's barrels (Winchester's too) are prone to having constrictions at the dovetails. It's possible that the previously mentioned ".306" measurement and currently quoted .3055" measurement are from the constriction, and not representative of the 'natural' dimensions. (I'm assuming it's the same measurement and you rounded before.)
As such, slugging just the end(s) of the barrel may provide more useful numbers.
For example: Run a slug into the muzzle end about an inch, then push it back out the muzzle from the chamber end.
And, if the slug(s) do show more 'normal' dimensions, it may indicate that your accuracy issues could be related to a constriction.


And, lastly...
I've never had much luck with egg sinkers. I no longer use them. How they enter the bore has a huge impact on the dimensions represented, and I've only had the dimensions match those taken from a pure lead bullet one time.
If you want a few pure lead bullets to use for slugging, send me a PM. I always try to keep a supply of pure lead slugs on hand, and should have plenty of .30s right now. (From .309" to .316" -- possibly sweetened with a little tin, but they're still plenty soft.)
Even if I don't have .30 cal slugs, I do have 3/8" lead wire that can be pounded to shape quite easily and rolled for smoothness between steel plates (if desired).

 

[gwpercle]

The rifle should shoot factory jacketed bullets, if they group poorly then it might be the rifle . Look at your muzzels crown...a nick, dent , burr or a poorly done crown (lopsided or oval shaped) could be causing the patterens.
If the rifle groups factory jacketed....try another cast bullet.
I use a 170 gr. FP ,size to .308 , cast from clip on wheel weights and always install a gas check...load to 1600 fps. Pushed too fast and the micro grooves can't grip the soft lead . The GC protects the base and I've never had a gas check hurt accuracy.
Bullet size, hardness and velocity is what you have to watch for, but you must check to see if it's the rifle . If it won't group the 170 Remington's ...it's something going on with the rifle .
Gary

 

[Wendyj]

So I took a round ball for my percussion muzzleloader and flattened it out and rounded best I could. Calipers hard to tell precisely but I had to tap it all the way through. Seemed pretty tight. Measurements are around .308.5 to .309. This is picture of slug. Measured with RCBS calipers.

So to chronograph a few rounds at 17.5 grains of H4895 average velocity is 1295fps.

 

[FrankenMauser]

Much better.
You probably had at least 5 tenths (0.0005") spring-back if it felt pretty tight and got trimmed that substantially on the way in.

I'm not suggesting you do such, since I didn't do the slugging; but I would consider that a .308" or .3085" rifle, based on my own experience.

 

[Bmp4510]

Much better.
You probably had at least 5 tenths (0.0005") spring-back if it felt pretty tight and got trimmed that substantially on the way in.

I'm not suggesting you do such, since I didn't do the slugging; but I would consider that a .308" or .3085" rifle, based on my own experience.

I saw a neat way to make lead ingots for slugging a barrel on the internet. Take one of your empty cases, and place the lead in the case. I bought some cheap muzzle loading balls that were pure lead. Once you cram whatever lead you can in the case, use a propane torch to melt the lead in the case. Tap your new slightly oversized “bullet” out of the case, and slug your gun with it.

Use your imagination as well. For instance, I use .357 to slug .380’s, 9mm, 38 and .357. You will find that this method makes a long slug that is easily measurable. Good luck.


Sent from my iPad using Tapatalk

 

[Wendyj]

Frankenmauser, so I guess if 308 or 309 then the .311 bullets are too big. Should I go with .310.. Only going to order a sample pack this time instead of 500.

 

[FrankenMauser]

Honestly...
I don't think it matters.
Other members here have far more experience with cast bullets than I do, but I don't think 0.002" oversized is going to cause problems. In my opinion: If it'll chamber, it's not too big.

I think this may just be an instance where the bullet doesn't like the barrel (or throat), there's a defect in the bore or crown, or the 'perfect' powder charge (and powder) hasn't been found yet.

 

[Wendyj]

I'm agreeing. I'm going to try some factory cor locs 170 grain this weekend. No better and I'm going to trade off and grab another Henry. They have done great in 44 and 45 for me. Hate to give up but I've got 2 months of trial and error in this one.

 

[243winxb]

Marlin micro groove vs ballard rifling.

Internet claims a cast bullet needs to be .002" larger then micro groove diameter. A gas checked bullet may grip the rifling better then a plain base?

Having had a 44 mag Marlin micro, accuracy was poor with .430" diameter plain base home cast swc bullets. Sold it.

My ammo worked great in my S&W M29. The idea was to shoot the same ammo in both guns. Didnt work out for me.

 

[YARDDOG(1)]

Try to fire lap the barrel before you get rid of it ,, Just a option ; )
Y/D

 

[FrankenMauser]

The rifle was sold today.
It was mentioned in another thread.

 

[Wendyj]

I melted the rest of the bullets I have and am going to send to a friend of mine to cast me some 45 colt with gas checks for my Henry. The rifle loves lead and I really enjoy shooting it. I had never melted any down so I grabbed a stainless skillet with the wood handle broke off and melted on a turkey fryer. Or my husband did. I'm a little leery of fire and lead. We pored into a muffin pan. I don't know if the lube hurt it or not. Read somewhere it would help flux it. I would like to cast my own but I don't know if I am good enough. Is the dark spots on these ingots the lube??

 

[T. O'Heir]

"...a rod and pushed the bullet through..." That alone suggests undersized dimensions. Too easy. Slugging a Lee-Enfield barrel, for example, requires the plastic mallet for the whole length. Should be a regular cast .30 calibre bullet without extra lube too.
However, like 243winxb says, the Marlin Microgroove technology has something to do with it too.

 

[Wendyj]

I re slugged with a round ball for my muzzleloader after the egg sinker trick and it slugged out .309 and was tight. I had to tap it all the way through. It's gone now so it doesn't matter anymore.

 

[Chainsaw.]

On your ingots, just some minimal impurities, will come out fine once inn a casting pot and fluxed.