.250 Slugs in a .248 Polygonal Bore?

[mtnGhost]

I've been thinking a lot about optimal slug-type ammo for my RAW's polygonal barrel. I confirmed the bore is .248" and the grooves are .254". I have this rifle tuned at 968fps / 70FPE right now using 34gr JSBs during power testing (cheaper and higher resolution for tuning with my chronos). 

With the 33gr VKs, my rifle produces 945fps with this current config; the 34gr NSAs are averaging 935fps. There's definitely some friction at work.

Remembering some discussions on caution for using hard cast ammo out of the 10mm Glock poly barrels (go-to bear defense ammo in the mountains), I'm starting to wonder if .250 might be too large for this barrel. I could certainly lap the bore down gently to reduce the friction or get molds to fit the bore a little more closely to its diameter.

What are your thoughts on using the denser .250 ammo out of this barrel? I'm all ears  

 

[2D1C]

ME TOO!

 

[jwrabbit123]

HI I been shooting and making slugs for decades , well First sounds like you have plenty of power , To check size push a half dozen pellets threw and measure them and the average is the diameter of the tightest part of barrel , then add .005 . and as for hardness any slug 6 BHN to 14 BHN is fine I wouldnt shoot anything harder then this

I use pure lead on some and some 95% lead and 5% tin .

you should be able to puush the slug threw your barrel with some pressure and slight markings on slug . this is correct size

I know any RAW has a highly finished barrel I would not touch it . they are very very good .

In stead if you buying slugs get your self a sizer like NOE push threw one /

Like you are shooting .25 calibers get your self a .250 .249 and .248 and have fun tuning

I think at your power try some heavier slugs like MP 48 grains and size to .250 .



LOU

 

[mtnGhost]

HI I been shooting and making slugs for decades , well First sounds like you have plenty of power , To check size push a half dozen pellets threw and measure them and the average is the diameter of the tightest part of barrel , then add .005 . and as for hardness any slug 6 BHN to 14 BHN is fine I wouldnt shoot anything harder then this

I use pure lead on some and some 95% lead and 5% tin .

you should be able to puush the slug threw your barrel with some pressure and slight markings on slug . this is correct size

I know any RAW has a highly finished barrel I would not touch it . they are very very good .

In stead if you buying slugs get your self a sizer like NOE push threw one /

Like you are shooting .25 calibers get your self a .250 .249 and .248 and have fun tuning

I think at your power try some heavier slugs like MP 48 grains and size to .250 .



LOU

Thanks Lou, I had pushed some through and measured them out to .246-.247. The lead is dense with those Nielsen's, but soft enough that I have to let them cool a little after pushing them through so my caliper doesn't bend the lead as easily.

I consider this stage of the tune stage 1. My end goal is definitely to shoot heavier ammo, since I'm always dealing with wind here. Nick Nielsen says that his friend has the same rifle / barrel and shoots 39gr slugs with "very high accuracy". I wanted to jump up to 40-42gr next, so that might also be a good stepping stone for me.

I like your idea of sizing too. Great advice man all around, muchos tacos amigo!  

 

[mtnGhost]

Did some experimenting today with 33gr Varmint Knockers, 34gr NSAs, and 34.7gr NSAs.

First, I think my regulator "woke up". I started filling closer to 250bar instead of 230bars. I thought my LabRadar was screwed up when I started seeing way higher numbers (965-985fps) than the speeds from my tuning tests (930-935fps)! I ran some over my EdGun chronograph and then my Chrony and verified that it wasn't wrong. 

Longer version short - today was once again VERY WINDY! I was pissed, expecting max wind gusts of 11-13, which wound up being variable gusts 28-37mph. I found out later in the day that the wind knocked over a massive construction crane downtown, pretty serious but status quo).

With the exception of the heavier 34.7gr NSAs (2S HP form), none grouped very well on the top end. I was shooting out to 104y, tried waiting in between shots for the wind to ease up, but I was on the side of a hill at a different shooting location today, and the variability was even worse than where I normally setup.

Here's what I observed with the 34gr out of my .25 RAW - loopy at 965-980, "ok" from 945-960, better / good from 925-940, really good (but HIGHLY vulnerable to the wind) below 920 (I did some field tuning and got them as low as 743).

I couldn't get the 33gr VKs to group well at all today, but I wasn't as granular with the as I was with the 34gr NSAs (I just had more of them with me today).

I laid down some solid hole in hole groups with the 34.7gr's and the 34gr in the wind. The 34.7's felt like JSBs without the randomness! The shape and mirror finish makes them easy to track through my scope (7-35 ATACR). I watched them lob one after another at the target, probably shot 90 of them today. I would get some random ones that took an immediate left after exiting my muzzle, and land a couple / few MOA to the left.

I went through 4350psi > 2950psi from my Great White 97cu/ft tank, having to fill my 480cc bottle after one mag. Very inefficient. I need to dial everything back down if I shoot this stuff again! 

From here, I'm not sure what to do. I can go heavier, but I don't want to have to deplete a 97cu/ft tank to shoot for half a day. My goal for this is to find ammo that will work well out of my barrel / rifle, that doesn't require a fill after one mag. Again, I'm shooting slugs for windy conditions and for long range when the winds aren't as brutal.

P.S. - For fun, I ran a few 25gr JSBs. They sound crazy over 1000fps

 

[mtnGhost]

These were the best groups today, 4 hand loaded 34.7gr plus one mag (12):

This was two mags of the 34gr NSAs..