Optimal caliber for ELR?

[badger5th]

I shamelessly copy clipped this from a PB forum page regarding ballistic coefficients of cast bullets:

Quote:
RCBS Cast Rifle Bullet Ballistic Coefficients
22-055 FN .159
243-095 .258
257-120 .272
270-150 .327
7mm-145 Silh. .272
7mm-168 SP .306
30-115 SP .175
30-150 FN .220
308-165 Silh. .286
30-180 SP .293
30-180 FN .255
35-200 FN .243
357-180 Silh .210
375-200 FN .220
44-200 FN .130
429-240 Silh .186
45-300 FN .207
45-405 FN .303
45-500 FN .365[/Quote]

I acknowledge my relative ignorance whether any of the above would be appropriate as an airgun slug although the .257 at 120gr may be useable. Decent BC for that caliber as well.

 

[Scotchmo]

…I acknowledge my relative ignorance whether any of the above would be appropriate as an airgun slug although the .257 at 120gr may be useable. Decent BC for that caliber as well.

A long range airgun projectile is best at high subsonic velocities. The sectional density of a 120gr .257 would make it difficult for an airgun to push at a decent velocity. High pressure + long barrel + inefficient + harsher. It could be done but might not be worth the trade offs, unless under very windy conditions, or at very long distances.

For 300yds, ~1000fps and BC>0.150
For 500yds, ~1000fps and BC>0.250

How far do you want to shoot?

 

[steve123]

Tell ya the truth it was disappointing, only because current fill apparatus will not allow me to shoot it simultaneously w/LDC & step down in-line reg. Maybe there's a shorter 45* QD FF that would allow clearance. This was the first time I had fired it with the .357 Emperor on it. Wish I could shoot it like that while tethered but no can do for groups. On a 3600psi fill it'll yield 3 shots that are predictable enough for varmint hunting of reasonable ranges. Thankfully there's no mentionable POI change with that monster can on/off. I highly doubt I'm going to buy a good thermal & hunt coyotes, but it's capable. I honestly wouldn't want to carry it.

I was laying prone and shooting at a 0* angle target 105yrds out. I wasn't as early as I liked and the wind had picked up let alone the mirage was pretty dam bad at ground level. I tried a Athlon Midas but I don't like the reticle. Went back to the SWFA 16X. Groups were good when I did good. I got 3 inside of 1" 3 times but that was out of like 60 shots.
Edit: I should say I started around 3200psi, dialing it in I saw as hot as 980fps but I settled at 3K and 944fps. I recently sold a compressor and probably plan on selling this because optimum speed is currently configured for a 3600psi fill, yielding 1080fps w/a 72 grain .2573" Griffing RBT. I could easily buy another big compressor (or see if a Hill pump cause a heart attack lol) but since I moved I just don't care to drag everything out. I use to be able to shoot 300-400 yards off my front porch. Believe me the Scandalous can shoot. IDK, maybe I will buy a Edgun or FX and just hand pump it once a week, turn it down to 12ft/lbs, get 300 shots.

It was just pretty windy, I should have a better scope & I am still not sure if all the others that I don't think I pulled were due to mirage, or more wind. So nothing great to show but thanks for askinView attachment 284530

Sorry it didn't go better. Keep us posted if you have any updates.

 

[badger5th]

A long range airgun projectile is best at high subsonic velocities. The sectional density of a 120gr .257 would make it difficult for an airgun to push at a decent velocity. High pressure + long barrel + inefficient + harsher. It could be done but might not be worth the trade offs, unless under very windy conditions, or at very long distances.

For 300yds, ~1000fps and BC>0.150
For 500yds, ~1000fps and BC>0.250

How far do you want to shoot?

Me? not more than 200 yards since that's the longest distance I can get in Eastern MA.

 

[Scotchmo]

Me? not more than 200 yards since that's the longest distance I can get in Eastern MA.

What’s optimal for 200yds with an airgun? If that were the longest distance that I intended to shoot, I’d look for about 0.1+ BC to start, but probably under 0.2 BC as the trade offs to get higher BC would not be worth it for that distance, at least not for me.

 

[steve123]

I shamelessly copy clipped this from a PB forum page regarding ballistic coefficients of cast bullets:

Quote:
RCBS Cast Rifle Bullet Ballistic Coefficients
22-055 FN .159
243-095 .258
257-120 .272
270-150 .327
7mm-145 Silh. .272
7mm-168 SP .306
30-115 SP .175
30-150 FN .220
308-165 Silh. .286
30-180 SP .293
30-180 FN .255
35-200 FN .243
357-180 Silh .210
375-200 FN .220
44-200 FN .130
429-240 Silh .186
45-300 FN .207
45-405 FN .303
45-500 FN .365

I acknowledge my relative ignorance whether any of the above would be appropriate as an airgun slug although the .257 at 120gr may be useable. Decent BC for that caliber as well.
[/QUOTE]

I wonder what the G1 BC would be for a 190gr 7mm pure lead slug, probably be in the .5 area?? also lots of friction as it goes down the barrel too.

 

[Scotchmo]

I acknowledge my relative ignorance whether any of the above would be appropriate as an airgun slug although the .257 at 120gr may be useable. Decent BC for that caliber as well.

I wonder what the G1 BC would be for a 190gr 7mm pure lead slug, probably be in the .5 area?? also lots of friction as it goes down the barrel too.
[/QUOTE]

A 190gr Berger 7mm has an advertised G1 BC of 0.75. At some point enough is enough. Those very high BC projectiles would be great if that BC did not come with a "high price". At subsonic velocities, it's just not worth it, in my opinion. Besides what I already covered, those long for caliber projectiles need a high spin rate. If you are shooting at ELR distances (300yds for an airgun?), your spin drift at the slow velocity will likely exceed your wind drift, and you will need to take that into account before you take an important shot. Your firing solution gets more complicated. If you get sighter shots, say for benchrest, or just going for a good group at a specific distance, than not so much of a problem as you can re-zero for the specific target. If you are OK with a 36"+ barrel length, 6000psi plenum pressures, and 1 shot per fill, then try it out.

 

[steve123]

I wonder what the G1 BC would be for a 190gr 7mm pure lead slug, probably be in the .5 area?? also lots of friction as it goes down the barrel too.

A 190gr Berger 7mm has an advertised G1 BC of 0.75. At some point enough is enough. Those very high BC projectiles would be great if that BC did not come with a "high price". At subsonic velocities, it's just not worth it, in my opinion. Besides what I already covered, those long for caliber projectiles need a high spin rate. If you are shooting at ELR distances (300yds for an airgun?), your spin drift at the slow velocity will likely exceed your wind drift, and you will need to take that into account before you take an important shot. Your firing solution gets more complicated. If you get sighter shots, say for benchrest, or just going for a good group at a specific distance, than not so much of a problem as you can re-zero for the specific target. If you are OK with a 36"+ barrel length, 6000psi plenum pressures, and 1 shot per fill, then try it out.
[/QUOTE]

I hadn't thought of the spin drift part.

At 300Y and putting your .257/.16 BC at 1000 fps compared to a 7mm/190gr/.5 BC going the same speed my ballistic app shows 1.7 mils of drift for a 10 mph wind for the .257 vs .6 mil for the 7mm. But I don't think my app compensates for spin drift.

What does your ballistic app show?

 

[Scotchmo]

A 190gr Berger 7mm has an advertised G1 BC of 0.75. At some point enough is enough. Those very high BC projectiles would be great if that BC did not come with a "high price". At subsonic velocities, it's just not worth it, in my opinion. Besides what I already covered, those long for caliber projectiles need a high spin rate. If you are shooting at ELR distances (300yds for an airgun?), your spin drift at the slow velocity will likely exceed your wind drift, and you will need to take that into account before you take an important shot. Your firing solution gets more complicated. If you get sighter shots, say for benchrest, or just going for a good group at a specific distance, than not so much of a problem as you can re-zero for the specific target. If you are OK with a 36"+ barrel length, 6000psi plenum pressures, and 1 shot per fill, then try it out.

I hadn't thought of the spin drift part.

At 300Y and putting your .257/.16 BC at 1000 fps compared to a 7mm/190gr/.5 BC going the same speed my ballistic app shows 1.7 mils of drift for a 10 mph wind for the .257 vs .6 mil for the 7mm. But I don't think my app compensates for spin drift.

What does your ballistic app show?
[/QUOTE]

I guess I still have more to learn. I ran some numbers. It appears that even though it needs a faster twist rate, the heavier, higher BC projectile does not have more spin drift. They are both in the 1+moa range at 300yards. The other disadvantages still hold (higher pressure + longer barrel + inefficient + harsher). The tradeoffs are going to be up to each person, based on their specific application.

I'm trying to move up a little from the .257 caliber, to a 7mm. But I'm only going with 96gr to 106gr with a 0.23 BC (hopefully). I hope to push it into the 970fps+ range (220fpe+) and still retain the docile feel of the .257. I did not see any way to do that with a much heavier 7mm slug. I am going to try an even longer barrel with the 7mm, but I can't safely go much higher pressure in this gun.

 

[mercado]

All the mold available in 7mm are .. lame or to heavy for a airgun so far .. the 96g looks good the 106g cannot compare to the 100g .. 257-418 .. or the rcbs 257-100 .. that nobody has tried to find tha twist to shoot stable ..my bad a 1-7 was tried but it didn't work either ..the 10 twists also didn't work.. tj has the tooling for a 257 - 1-8 twist I also paid the tooling for a 257-1-9 to be made..because that is the bullet i want to be able to use .. They will be also tooling for 224 .. 1-8.5 and 1-9.5 ..would really like to know what the bc for the 257-418 is..Scotchmo .. do you have the 257-418 ..? Could I send you some so we could know what the bc is.. I really use my 257 ones a year if I'm lucky.. but still I have another complete buid only waiting for the 1-8 n 1-9 barrels to test..

 

[mercado]

I found one's the only mold in its kind..B&M iron 178g boat tail spizer that is something to look at but I try it in my texan and even at 10y it made key holes ..in order to be able to use it I would had to go head on in a custom build..I was not aviable to secure a valve build. So I see no point to continue..sold the mold and the rifle.. n decide to stay with small calibers..I keept a few cast bullet so if a custom valve is made I could order a mold to be made..the first is another reare mold of the same manufacturer B&M in 257 weight is 95g the big bullet below is the 308 - 178g

 

[Scotchmo]

I found one's the only mold in its kind..B&M iron 178g boat tail spizer that is something to look at but I try it in my texan and even at 10y it made key holes ..in order to be able to use it I would had to go head on in a custom build..I was not aviable to secure a valve build. So I see no point to continue..sold the mold and the rifle.. n decide to stay with small calibers..I keept a few cast bullet so if a custom valve is made I could order a mold to be made..the first is another reare mold of the same manufacturer B&M in 257 weight is 95g the big bullet below is the 308 - 178g...

I really needed a heavier projectile, but the >90gr .257 projectiles would be increasingly difficult to push, and would likely need faster twist than 1:14 for optimum performance, so a new barrel. If I had stuck with the .257, I would have likely used the 92gr "Noble" slug. At this point, I'm looking to build an airgun that works well out to 400yds and has well over 200fpe of muzzle energy. The 1:14 .257 can go the distance but the fpe would be marginal. I'm going with 7mm. If I did not need more than 200fpe, I would stick with the .257.

A 178gr is way to heavy for me. I ordered the following molds for my 1:14 twist, 7mm build:

7MM - 96 Grain FN "Bowman"

arsenalmolds.com

284-106-FN-BX6 4 Cavity RG4 BT | NOE Bullet Moulds

noebulletmolds.com

The 106gr 7mm NOE mold is a brand new offering. It is not "lame" - that's my opinion. It looks optimal for a long range airgun.

My gun was really designed for calibers between .25 and .30. with a 0.750" maximum projectile length. I considered doing a .308, and even that would probably work well enough, but decided to try a 7mm (0.284) as it seemed to be a better choice for my current needs.

 

[mercado]

Yup a faster twist is needed that is why I paid for the new tooling to be able to have the option to test 1-8 and 1-9 twist fot the 257 ..in my case I use airforce guns with a 33 inch barrel I could push 100g ..1050 fps at 3100 psi all day long.. a 7mm texan should be able to push 100g close to 1100fps.

 

[JungleShooter]

Gents, as I follow this thread it becomes increasingly and painfully clear: You guys are plain NUTS!!




When I grow up, I want to be like you.






So, what other threads should I be reading?
What guns should I be looking for?
What money are we talking about here?

And... — if I wanted to reign in the insantity just a bit — and shoot commercially available slugs — what caliber and what gun would do that for me? How "custom" does it have to be?

➔ Not to derail this thread, I'll start a different one for your replies, here:

What gun, caliber, and mods are needed for shooting commercially available slugs at 300y+?

What caliber, gun, and mods are needed for shooting commercially available slugs at 300y+? So, if I wanted to play this extreme long range game, but just not quite head-first-down-the-rabbit-hole as some of my ExLR heroes... — what does it take? 🤔 🔸(1) First of all: At 300y I'd like 2 to 3...

www.airgunnation.com

Thanks!

Matthias

 

[steve123]

I hadn't thought of the spin drift part.

At 300Y and putting your .257/.16 BC at 1000 fps compared to a 7mm/190gr/.5 BC going the same speed my ballistic app shows 1.7 mils of drift for a 10 mph wind for the .257 vs .6 mil for the 7mm. But I don't think my app compensates for spin drift.

What does your ballistic app show?

I guess I still have more to learn. I ran some numbers. It appears that even though it needs a faster twist rate, the heavier, higher BC projectile does not have more spin drift. They are both in the 1+moa range at 300yards. The other disadvantages still hold (higher pressure + longer barrel + inefficient + harsher). The tradeoffs are going to be up to each person, based on their specific application.

I'm trying to move up a little from the .257 caliber, to a 7mm. But I'm only going with 96gr to 106gr with a 0.23 BC (hopefully). I hope to push it into the 970fps+ range (220fpe+) and still retain the docile feel of the .257. I did not see any way to do that with a much heavier 7mm slug. I am going to try an even longer barrel with the 7mm, but I can't safely go much higher pressure in this gun.
[/QUOTE]

I'm agreeing with you Scott.
Air consumption, the power to push hard, in various bore diameters, really long lead projectiles, with correct twist rates, all add up to, enough is enough?!

It's still just interesting if someone could ever figure it out.

I tried 30 cal 230gr Berger Hybrids going 1050 fps in my 300BO with a 7 twist and its still not easy to hit steel 400 yards away. The vertical was just as much a problem as the wind drift because it was hard to keep the ES low. I also tried 225gr Hornady which at Mach 2.5 IIRC had a .77 BC without great success.

For whatever reason, perhaps lead projectiles and lots of bullet lube, my friends with black powder, 45-70's, and 535gr cast bullets had way more success at distance than I did with my 300BO?!

It's just that I have lots of lead, a good compressor, and convenient places to shoot long distance, so there's some motivation to try a powerful bigbore-ish pcp.

 

[Scotchmo]

Steve,

My .257 holds together well out to 300m. I can hit the high power pig silhouettes at 300m (328yds) consistently. But the Turkeys at 385m (421yds), I hit 1 out of 5, though I've only tried it once.

For subsonic shooting at ELR, any significant velocity spread is a problem. I've shot a 25 shot string and gotten a 975fps average muzzle velocity, SD = 2.8fps and ES = 10fps. A string like that gives me confidence. ES is marginally useful. I like the SD as it can be used to predict probability of keeping my vertical POI on the target.

 

[JackMan1]

Wow, ton of good info here. TY

 

[Believer12]

Agreed, lots of good info