Figuring out proper bore fit

[brewer12345]

I started casting for 38 special because I had been using commercial .358 lead fodder and knew that size would work. My next effort will be casting for a 35 Rem Marlin. Since I have only every shot factory jacketed in this rifle, I have no idea what the bullets should be sized to. So as I understand things, I need to slug the barrel and then size to the diameter of the grooves. How do I do this without messing up my rifle? I recently read that a .375 muzzleloading ball may be involved.

[Rcmaveric]

Light lubricate a bullet and gently pound it down. Lots of different ways. I am a fan of chamber pound cast. Then filling then throat of the chamber with the biggest bullet i can. To each their own and the gun will tell you what it likes through experimentation. I had decent results with .002 over groove diameter from a barrel slug. I used an old bell fishing weight. However i have gotten my best results filling the throat which i got from a chamber cast. Chamber cast can give you chamber dimensions aswell as your groove and bore. Searching you tube for chamber casting ( theres three different ways via pound cast, sulfer cast, and cerrasafe) and barrel sluging for videos.

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[Wayne Smith]

Use pure lead to do this. If you are measuring in the hundreds of thousands of an inch the springback from a harder lead will mislead you.

[lotech]

I won't argue with those who prefer to slug barrels as I'm sure the procedure has at least some merit in a variety of situations. During the last several decades, I somehow wound up with quite a variety of bullet sizing dies. I usually try several diameters until I find the largest that will allow chambering a loaded round without difficulty. This diameter generally provides best accuracy. I've never had a .35 Remington. .358" might work, but I believe I would initially try .359" and .360" bullets.

[brewer12345]

I won't argue with those who prefer to slug barrels as I'm sure the procedure has at least some merit in a variety of situations. During the last several decades, I somehow wound up with quite a variety of bullet sizing dies. I usually try several diameters until I find the largest that will allow chambering a loaded round without difficulty. This diameter generally provides best accuracy. I've never had a .35 Remington. .358" might work, but I believe I would initially try .359" and .360" bullets.

What happens if you use a slightly too-big bullet? Poor accuracy? Lots of leading? Potentially dangerous?

[mdi]

I like to know my guns. Slugging is esy and safe. Don't use a steel hammer, no matter how careful you are you could damage the muzzle. As noted above use a soft lead slug (a muzzle loader ball should be soft enough) at least .010" over groove diameter (for a 357 Mag, use aat least a .367" slug). Lightly lube the slug and the barrel and start the slug into the muzzle with a leather, plastic mallet. Once flush use a short brass rod to start the slug (just like a muzzle loader). Use a brass rod to drive the slug through the barrel. I prefer a heavy hammer to "push the slug through rather than a "tap-tap-tap", a 1 lb. dead blow hammer will work well. I like to do at least three slugs through the barrel just for consistency. Measure slug with micrometers...

https://www.mcmaster.com/#standard-brass-alloy-rods/=19p182z 5/16" dia is a good size for a .357 and will work with larger calibers too. You might find 6' lengths a bit cheaper with a google search "brass rod". Don't use hardwood dowels as they may split and can jam in the bore.

[NoAngel]

Fit to the throat, forget the bore.

[quail4jake]

You may want to check out Veral Smith's LBT website, check out the lead chamber throat slugging part. Very worthwhile and really works. Filling the throat and getting the ogive base into the rifling lead seems to be a mechanical fit that works well, you may also consider a bullet with a bore riding nose.

[lotech]

What happens if you use a slightly too-big bullet? Poor accuracy? Lots of leading? Potentially dangerous?
I suppose if you used a very hard bullet that was grossly oversized with a hot load you could run into trouble. I wasn't referring to such a rare and exceptional situation. Handloading requires a degree of competence. I doubt you would find anything chambered in .35 Remington that had bore, throat, or ball seat dimensions that were far off SAAMI specs.

About ten years ago, I spoke with a ballistics/ engineer guy at Lyman about this very thing. He said pressure variations were quite small when changing bullet diameters with cast bullets, but he was speaking of small variations such as going from .357" to .360" as this is what I had asked about, nothing radical.

I have seen a decrease in accuracy with both oversized and undersized bullets in handguns and rifles. I don't recall an increase in leading with large diameter bullets, though it may have happened in isolated instances. Too small a bullet and leading and poor accuracy is pretty well guaranteed.

[quail4jake]

Fit to the throat, forget the bore.
"Bring the cannolis, leave the gun" -Pete Clemenza (LOL)....Thanks, this is a great quote and the truth! Sounds like Veral Smith's advice.

[gwpercle]

Back in the dark ages (1960's) we didn't know about slugging , so we went to the Lyman Manual and checked what they did.
35 Remington
Test rifle: Marlin 336
barrel length : 20"
Twist : 1-16
Groove dia : .357"

Cast boolits : sized to .357

We would start sizing our boolits .357" or .358" and see how that worked.
Usually it worked fine. I reloaded for 45 years using this method and it worked well.
About 5 years ago ( after joining CB site) I got a measuring tool (caliper?) and slugged some barrels just because I was ashamed to admit I had never done this , bores were standard sizes and my sizing diameters were fine. I have never had any accuracy or leading problems so Lyman's recommendations must have been good.

For the 35 Remington I would start with a .358 sized boolit , Marlin micro groove rifling seems to benefit from little fatter boolit, see how they work.
Lyman recommends mould #358315 a 206 grain RN but I prefer a flat nose like
NOE 360-200-FN GC...with a tubular magazine I want a flat point .
Gary
I don't care for slugging either

[NoAngel]

"Bring the cannolis, leave the gun" -Pete Clemenza (LOL)....Thanks, this is a great quote and the truth! Sounds like Veral Smith's advice.


He's not wrong. I do a chamber impression with a pure lead bullet and a fire formed case. It tells me MUCH more than any bore slug ever will. It's about as close to 100% as you're gonna get. There's always that odd ball out there with some wonky internal dimensions but as a rule, When you fit to the throat and NO unsupported bullet, magic things happen.

[sqlbullet]

What happens if you use a slightly too-big bullet? Poor accuracy? Lots of leading? Potentially dangerous?

As long as the loaded round is within specification and drops freely into and out of the chamber, nothing. Doesn't take much pressure to size a lead bullet down a bit.

[sniper]

I got a bit frustrated, trying to slug the bore, and then measure the 5-groove slug with my caliper. I guess I didn't hold my mouth right, or something! I bought some .0002 minus range rods... .356, .357 and .358. In both my old and new .357 ,the .357 rod goes into the cylinder throats with no problem. If I lubricate the .358, it slides right in, with a bit of help. Close enough for government work, and my needs!8-) The .356 won't enter the barrel!

[mdi]

What happens if you use a slightly too-big bullet? Poor accuracy? Lots of leading? Potentially dangerous?

I've read of Schuetzen shooters using cast bullets as large as .010" over groove diameter and seating them into the rifling...

[NoAngel]

I haven't went as far as 10 thousandths but my .30 Badger shoots like a house fire with .311 bullets and the barrel is .308(ish) 3 thousandths over is a little on the heavy side but it works so we ain't rocking the boat.

The one thing I have noticed, the increased friction of a tighter press fit can make the barrel heat up faster. When i was tinkering with a .308 Winchester I noticed a .311 bullet heated up the barrel much faster than a .3095 Neither gave any signs of pressure.

Everyone is different and there can be no denying that bore riders can be accurate but I will not use them. With higher pressure loads the bullet nose can engrave more on one side than the other causing it to wobble and thereby affecting accuracy. Each to his own. I stick with what works for me.

Seriously though, fill the entire throat and use a well supported bullet as much as possible.

[Menner]

Marlin 336 in 35 Rem
Get a RCBS 35-200 mold, size .359 and put the appropriate powder behind it and watch one hole appear
I have slugged barrels, not hard to do just make sure soft lead and lube barrel found most useful with milsurp rifles as they can be all over the place but only slug a commercial rifle if I see a problem using the standard specs. I have seen accuracy go south with using a way over sized bullet even if it fits the throat only testing will tell the real story
just my 2 cents
Tony

[gpidaho]

Don't worry too much with slightly over sized bullets (the cast ones) while it is surely not recommended. I have personally seen a 357 mag round sized .358 accidentally fired in a 30-30 Handi rifle. No damage was done to the rifle and the bullet actually hit the target although splitting the case end to end. Gp

[Yodogsandman]

Slugging your chamber and measuring will always be the best way. The quick and dirty method though is to measure the inside of the case neck from a case that's been fired it that rifle.

I had a couple of military surplus rifles with long, worn throats that drove me crazy and a pound slug didn't show the true throat diameter. On a whim, I tried as cast size boolits in dummy rounds and they fit the throat without effort. Tried these boolits in a fired case and they slid in. So, I always check the inside case neck diameters now, too.