Lapped with JB test

[Mram10us]

I have a 300wsm that seems to be a little slow. I shot 210vld with 69 r26. Thinking I might have a rough bore, I used JB bore paste to try and lap with 20 strokes of a jag and tight patch. Mixed JB paste with transmission fluid and sure cleaned the bore.
Before:

After

Next up is pouring a slug and lapping to see what happens with speeds

 

[dirthead1]

How many rounds do you have down the barrel? It will probably speed up a good bit somewhere around 100 rounds.

 

[Mram10us]

About 150

 

[Jud96]

You're doing more harm than good. Is this barrel copper fouling bad? Just shoot the thing and see if it speeds up. Some barrels take more than others to speed up. Are you loading a max load and seeing pressure and getting slow speeds? Just because someone else got 3000 with the same powder charge or your old barrel was faster doesn't mean you'll have the same results. Slow barrels are a real thing, but trying to lap it yourself to speed it up isn't going to significantly help. My cousin has a 300 WSM and 2830FPS is what we got with around 68gr of RL26 and a 208gr ELD. I don't think your results are that far off what should be expected.

I'm sure I'll get some opposition, but lapping a barrel can harm it if you don't have the proper tools or know the proper techniques to do so. The crown and throat/chamber would be the major things I would worry about damaging when trying to lap a barrel that's already fitted and finished. I'm not trying to be negative, I just want to help prevent anymore problems from happening.

 

[Wedgy]

As stated I think you are jumping the gun a little, just do a good stripping and continue break in. I have seen the WSM do a little better with .003" neck tension.
As far as JB/Isso I just started the VFG pellets and like them, the long jag adapter can hold 3 felt pellets.
https://www.brownells.com/gun-clean...ts/weapons-care-system-pellets-prod13839.aspx

 

[Tucker65]

I'm shooting 210's in a 24" barrel with 67gr of Reloder 26 and getting 2850 fps. Probably 250 rounds down the tube.

 

[sedancowboy]

20 strokes with JB Bore compound is not going to make a difference. I have a bit of experience with this and it takes at least 100 strokes to make a difference checked with a bore scope. I too use the VFG pellets and a 3 pellet jag.
I would not lap with a lead lap and lapping compound you will surely ruin the barrel. The problem is where the lap changes directions will be larger than the bore.
If I felt I had to do something drastic to the bore I would use something like Tubbs finial finish at least it is going only one direction.

 

[Alex Wheeler]

Jb is not lapping compound, and 20 strokes would not be measurable. Bore dimensions have a large effect on velocity, but lapping is not the way to change them, its a way to uniform things. You wont be able to avoid rounding the sharp edges of the lands if you lap too much, and that will cause a loss off accuracy. If its an experiment, go for it. But if the barrel is accurate, Id recommend shooting it a little slower.

 

[Blancoalex]

sedancowboy, can you share your experience of using the vfg pellets. What was gained using these?

 

[sedancowboy]

They fit tight in the bore and hold the jb well.

 

[Ross1147]

Honestly I think you are in the ballpark if it's a SAAMI chamber stock gun? I have a custom chamber 10 twist with a 26" proof and I'm running the 200.20x at 2932fps with 69grn of RL26. After testing, mine liked .002" neck tension. I was able to hit 3002fps (can't remember charge but sticky bolt) so I backed it off a grain or so and settled with the speed listed above. Add 10grn of bullet and 2" shorter barrel and 100fps less sounds about right? No animal is going to complain about a 210vld moving at 2830fps.

 

[tankgijohn72]

Shoot it, it will speed up. Maybe not as much as you want, but it will go faster. As the barrel wears, the roughness in the throat increases the chamber pressure/MV. If you want more velocity try different powder or increase powder charge, leave the bore alone.

Also, don't recommend going heavy with the JB bore paste. Did some testing in lab environment with one of the bigger 30 cal cartridges. Every 100 rounds cleaned heavily with 30 strokes of JB. Velocity increased through 500 rounds even as bore dimensions both lands/grooves opened up (measured with laser bore mapper). Avg velocity increased even though bore dimensions were getting larger due to the JB bore paste regimen.

 

[Wachsmann]

Its not a 300 RUM or a 300 PRC. I burn 20 plus more grains just to get about 3100 FPS out of the RUM. If its a stock rifle it right at the speed it should be at.

 

[6.5-300 BEE]

The barrel makers will luv you. Suggest you use 60 grit compound and fire lap to speed it up even more.

A 210 gr @ 28-900 is normal to fast for a 24" 300 WM.

What do you need a 210 gr for ?