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After picking up a bore scope to try and figure out some issue with a 6.5 CM I decided to run it down the M70 .243. I wanted to check the bore knowing how quickly the barrel heats up. Its typical load in an 85gr InterBond at 3166 FPS that is fairly reliable to produce around 1/2" groups at 100 yards. I have been using H4350 in it and have noticed in other rifles that it runs hotter temperature wise than some other powders do. I also do not know the history of this rifle prior to when I purchased it used.
To say I was surprised would be a slight understatement. I was expecting some evidence of heat, but not what I found. Maybe this isnt as bad as I think, but it sure doesnt seem good.
Throat
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1/2-3/4" down the barrel
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1.5" down barrel
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That is on my list of things to do now. This is my hottest running rifle though based off of memory. I also do not know its previous owner history. I personally dont have that many rounds through it.
It won't keep me up at night. I have two replacement barrel options already if it comes down to it. Both used be on .244 H&H rifles and will need the chamber cut off and redone for use as a .243. Both are currently on the heavy side and one is stainless.
I plan on a good scrubbing before the next time it goes to the range to see how it shoots. It's a bit overdue for a cleaning anyways. If it still shoots I'm not going to worry about it for now. I don't see any reason for it to not still shoot well. I wasn't having major issues before other than the groups opened up last outing. I assumed it just needed a good scrubbing. Maybe that's is all it needs.
I googled borescope diagnosis. Turns out the alligator skin in the throat are called heat cracks. Doesn't appear to be uncommon to have a little. The article I found showed an AR gas hole that was oval. . Looked just like mine.
Its throat erosion. I just dont know how bad is actually bad. When you think about it, you are forcing high temperature and velocity gas and debris through a small hole. Steel can only take so much abuse before it starts to give. I was expecting some cracking and erosion in the throat, just not that much. Again, I do not know the prior history of this rifle before I purchased it. Maybe the previous owner shot thousands of rounds through it and didnt care, or maybe thats just what I should have expected with this chambering. I was just surprised at what I saw.
I did check a couple 6.5s, .30-06, .300WM and my little .458 just to compare. All had some degree of micro cracking in the rifling and the .30-06 had some slight cracking in the leade. I am not surprised on the .30-06 since I used to push it really hard with 180 gr and still push it with 150gr.
Oh that’s not bad. I’ve seen much worse! Your rifling is still good and sharp. A couple of shots after deep cleaning will fill those micro fractures with jacket material and it’ll settle right back down again.
I did a quick scrub and most of the build up in the bore is gone. I will have to get some rounds loaded up to see if the groups go back to about what they were previously.
I have a Mod 70 Heavy Varmint in .223 Rem (bought used) that I use as a pdog rifle. I have no idea how many rounds went through it when I bought it. But I know I put at least 14,000 through it myself. It was a very reliable pdog slayer out to 500-600 yards. I also own a HawkEye borescope, and saw much the same as you are seeing. Concerned, but I had a couple back-up rifles, So no need for immediate action. Accuracy didn't seem affected. Until it was.
I was shooting pdogs one day and while I was hitting 400-500 yard dogs as normal for the most part, I missed about 1 out of 5 at that range by 5 feet or more. Something was amiss.
When I got home that night, my Tipton cleaning rod went 8" down the breech before it started rotating. Upon borescope inspection, I found I had practically no rifling left for the first 8".
This happened between one shoot and the next. IME, when barrels go south...they do it quickly.
My advice....have a backup gun and shoot "Old Reliabe" until she doesn't.
This was thought of as a potential pronghorn rifle for a future trip. For now it may remain as a possible up North doe rifle. I cant use it for deer where I normally nap in the woods. I have other options for pronghorn already and so if I have any concern about it before a potential trip I will just take something else.
Having never run a bore scope down a barrel until quite recently I just never had a chance to see what the throat of any of my rifles looked like. Maybe this is normal and just fine for this cartridge, or maybe its on a rapid decline. I honestly dont know. I was expecting some cracking in the rifling, just not the leade to look like a 2x4 that has been in a fire pit for a while.
Freezer wrote: ↑Sat Jul 29, 2023 10:58 am
Put that bore scope away! It's making you crazy and twisting your thoughts. If that 243 is shooting 1/2 moa take it and hunt with it.
It was shoved down the bore of the .243 as a curiosity. I assume the change in group size I experienced was due to needing a cleaning. If it shoots like before after a cleaning im not going to worry about it until it becomes an issue at a quicker frequency. Nothing else I have that I have looked at with the scope looks anywhere close to how the .243 does, but I do not know how bad is actually bad. The reliable look down the bore at a light to see how shiny it is method doesnt show any issues.
This is more of a curiosity as to what those here with more knowledge than I have to say about it.
I can take a piece of metal I’ve machined with an AMAZING finish, it looks good feels good is good.
Look at it under magnification and it looks like ass.
Just shoot it till it won’t.
“The shepherd slaughters more of the flock than the wolf ever will.”
That's the current plan. I'm just going to take it easy on the rifle when I do go to the range. I could do 50 rounds in a range secession with the little .458, but not enough time to do that with the .243 if I avoid getting it too hot. Guess that just means I have an excuse to really work up a load for the M98 6.5 Swede. Current promising load is a 129 InterLock at 2750fps using H4831SC. It came in just over 1/2" C-C, but it's not a nice shaped group. Could have been wobble though..
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My pronghorn rifle is a 6mm Rem (.243 on mild steroids) with a healthy dose of H4350 under a 95 grain NBT. Launches at 3250 FPS. I've dead-dropped pronghorn a quarter mile away with it. Just a tip.
Last year I used a .30-06 launching a 150gr InterLock at 3100 fps using IMR4064. Worked really well at 250 yards.
6mm Rem was also another option when I went looking for a 6mm rifle. To me its a toss up between them. The M70 .243 just came along first. I like how the 85gr InterBond shoots, but I may go back to playing with the 100gr InterLock. I think I topped out around 3000 fps last time I played with them. Not sure a Pronghorn is going to tell the difference between an 85gr at 3166 fps and a 100gr at 3000 fps at any range I have business shooting at.
. Looked just like mine. 
