What kind of difference in groups will I see changing BH?

[Tripplebeards]

I was out to the range the other day and shot sub MOA at a 100 yards using my ruger 77/44 and a Lyman devastator loaded with a BH of 7.5. It was loaded with 21 gr of h110. I also shot a 1.2" group with a load of 23.8gr of w296 using the same boolit with a BH of 13.5. Both boolits are PC and GC.

How will my groups be affected if I changed to a harder or softer alloy with these loads? I was thinking of trying a little harder BH in the sub MOA load with both 10.5 and 13.5 BH boolits and wondered if it would tighten or open my groups up?

http://i.imgur.com/VxP3fgB.jpg

http://i.imgur.com/FrVlEJF.jpg

[vernm]

Why not run a test with the two boolits at the lower powder charge (velocity) and another test with the two boolits at the higher powder charge.
You may find that velocity makes more of a difference in group size than BH.

Oh. If you were just "fishing" for a compliment, nice groups.

[Tripplebeards]

Thanks, that's the plan. Was hoping someone already has done a similar test that could share their results.

[sqlbullet]

Depends on too many barrel specific factors.

[Tripplebeards]

No one else?

[Rcmaveric]

A lot goes into it. It depends on how hard you plan on shooting them and how well that bullet fits. If the fit is good and launch isn't high pressured then i think your softer bullets will be more accurate. If your fit is a little loose and your shooting for high velocity then you may need a harder bullet to prevent leading and hold up to the pressures. Wont necessarily be more accurate. It just wont lead your barrel.

[fecmech]

IMO you won't really know till you shoot more shots per group (at least 5, 10 is better) and more of each group. To really see any difference I would shoot at least five, 5 shot groups of each, alternating between the BHN's at the same time. I would not base my results on one or two 3 shot groups.

[Tripplebeards]

i tried two harder alloyed boolits today at a 100 yards. My rifle did not like them. The same 12gr H110 sub moa load with a 7.5 bh bullet opened up quite a bit with harder alloys. I tried bh of 10.5 and 13.5. Both harder boolits shot 3" plus groups. The 13.5 bh boolit dose better at higher velocities and will shoot 1.24" groups at a 100 yards with 23.8g of W296.

[Harry O]

You have good accuracy there. That means the bullet is hard enough for the pressure you are shooting at. It looks like the barrel, chamber, and throat dimensions are probably good, too. Reducing the Bhn will not change the accuracy very much until it gets too low. At that point, the accuracy will go bad very quickly. Increasing the Bhn will not change the accuracy very much, period.

From my experience, accuracy reacts to the Bhn in a major way at one point (and ONLY that point). When working up a load, that is when the pressure gets too much for the base of the bullet and deforms it as it goes down the barrel. Below that point, the accuracy is good. Above that point, the accuracy is bad. Usually, leading starts above that point, so you have a warning before leading occurs. Remember that hardness and strength are directly related. When you are discussing Bhn, you are also discussing the strength of the bullet. The only question is, is the bullet strong enough to handle the pressure of the gunpowder.

[Grmps]

You may find that the harder you push something the harder the alloy needs to be. also with the harder alloy, you need to push it hard enough to obturate.also if you have a softer boolit 3 thou over bore diameter you can push it harder than one 1 thou over bore diameter. The trick is to find the perfect combination for each gun of alloy, diamiter and velocity then-- fast or slow powder also comes into play. you run a lot of 5 shot ladder tests until you get close to perfect then finish with 10 shot ladder test.

http://www.lasc.us/Fryxell_Book_Chapter_3_alloySelectionMetallurgy.ht m

https://i.imgur.com/Cf4PQXQ.png

[Tripplebeards]

Well as you see in my post I tried the harder loads with the lighter charge of 21 gr of H110. The harder alloys must not have had enough pressure to force the boolit to "swell" up a little grab the rifling like the softer 7.5bh boolit did causing groups to open up. How about the opposite? My 23.8 gr load of W296? If I went from 80/20 down to the 50/50 mix or even softer 16:1, 7.5 BH what could I expect in accuracy changes?

I would assume the chart above doesn't apply to my load since I PC and GC as I'm running great accuracy at 1675fps with a 7.5 BH boolit.


My 16:1 mix ended up at 7.5bh which is my most accurate load. I mixed this with 16 lbs of pure and a pound of pewter. I would assume my pewter has a a lot of PB content so my boolit ended up be softer. Same with my accurate 80/20 mix. I added 6% pewter.

I have about 10 lbs of various 3 oz pewter blocks I melted for this and then I'm going to start using the genuine pewter halmarked items I have started to stockpile. So I'm worried that it is going to cause my BH to climb. I would assume in my future batches after I run out of these pewter blocks. I will need to test my alloy in the future to make sure it's the same hardness or accuracy will change.

I would assume a 7.5 BH alloy is a 7.5 BH alloy and it should characteristics should act the same going down my barrel?

My question is if one day in future when I use a different pewter alloy that has more tin content in it and let's say not enough of what ever mystery alloy was in the last pewter mix, as long as my boolits have a BH of 7.5 I would assume accuracy would be the same?

[Harry O]

From my experience, mixes of different materials, but with the same Bhn do not act exactly the same. Both antimony and tin raise the Bhn. But tin is better for accuracy. It is also more expensive.

Antimony raises the Bhn faster and farther than tin does. However, it is brittle, hard to fill out the mould, and leads the barrel easier. Tin does not raise the Bhn very fast and peaks out at a lower Bhn than antimony. However, it makes the mix very ductile, easy to fill out the mould, and is less likely to lead the barrel. I generally use equal amounts of antimony and tin. Sometimes more tin than antimony if the mould has a complicated shape (like hollow-base or hollow-point).

Bhn tells you a lot, but not everything. Think of it as one of many clues.

[Tripplebeards]

Good to know. Looks like I'm going to cast up till I use up the current l pewter blocks I made and stock pile my boolits so I know they are all the same alloy mix.

[Tripplebeards]

My plan is in the future is to test the hardness first instead of after and if my bh is harder than previously with using pewter ill dilute it with pure lead till it matches the hardness I am trying to achieve. I would assume accuracy will be close to identical this way.

I would assume it would also help to melt all my pewter together instead of a couple pounds at a time so the hardness won't vary

[popper]

Yes, an unknown additive like pewter I would make a single batch - Later accumulations go into a different batch.
You get a base deformation problem, a flow into the grooves or a (large dia.) pushed/cut away from the lands. BHN (alloy) affect all of these (as does boolit weight - inertia) so it is an experiment to see what works for your gun. The alloy has to be tough enough to prevent stripping and gas cutting during spin-up.