What's the difference between .25 cal. vs .257 cal. airgun ammunition?

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.257 usually referring to a slug or bullet, but also can refer directly to the exact size of the bore .25 is one of those generalized bore size ... This is only an example not a statement of fact but a Marauder .25 bore size might me a .253 and an AirForce .25 might be a .251. this is one of the reasons why some pellets shoot better out of different guns. It's when you move over to shooting bullets that knowing the actual bore size can make a big difference in performance 
 
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I own many .25 cal. airguns, but no .257 cal..

Is there any difference between the two, or is the .257 cal. designation just a manufacturer's sales gimmick?
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Massive difference, as its mostly slug bullet they're talking about in .257cal.

Take the new JSAR Raptor in .257cal @ 160fpe. .257 probably the most accurate longest range in air guns so far...

Still waiting on my .257, can hardly wait to try some .257 Caliber, 107 gr.
 
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I just got off the line with Travis at JSAR after asking a group of questions to him regarding the Raptor. I'm seriously considering ordering one in the next few weeks. He's a nice guy and took the time to answer everything I had to question. It's always nice to get a discount and free shipping whenever I can, and being a veteran, which I am, pays off at JSAR in that respect!

As long as we're talking about the Raptor, I wonder if anyone reading this has one and can offer his opinion of the product, the build quality, and the service at JSAR?
 
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From online post I have seen there has only been one .257 Raptor delivered. It went to David "Rocker1" on GTA. He has not post up much on it.

The Raptor will most likely not be accurate shooting a 107gr bullet. The bullet will be to long for the 1:14 twist rate barrel to stabilize, plus at 160 fpe it will not push it very fast...maybe 800-825 fps.

I think an ideal bullet will be in the 60-65 grain for the Raptors power and barrel twist rate.


 
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From online post I have seen there has only been one .257 Raptor delivered. It went to David "Rocker1" on GTA. He has not post up much on it.

The Raptor will most likely not be accurate shooting a 107gr bullet. The bullet will be to long for the 1:14 twist rate barrel to stabilize, plus at 160 fpe it will not push it very fast...maybe 800-825 fps.

I think an ideal bullet will be in the 60-65 grain for the Raptors power and barrel twist rate.
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Should have my .257 barrel kit for my Texan beginning of the week. It is 1:14 as that was the only option, didn't see a 1:10 option that probably would be better for heavier longer ammo. Got a decent assortment of slugs to try. Thanks for the good info on 1:14 twist rate ammo preference.

Sorry if I confused anyone, I do not have a Raptor (yet). Was just using it as a .257 example. As we've all seen its advertised specs, that we really don't have any reason to doubt, as far as I know. Travis has always been a straight shooter with me.

jmo
 
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Here is a good reference for looking at barrel twist vs bullet parameters.

The inputs for this example are for a .257 cal 105gr bullet from an NOE mold. Best to be above 1.5 for stability factor and out of thr trans sonic speed range. Looking at the graphs you can see it will by the numbers not be stable.

http://www.geoffrey-kolbe.com/cgi-bin/barrel_twist.cgi?diameter=.257&length=.860&nose=.360&meplat=.130&base_diameter=.257&angle=&boat_tail=&b_twist=14&secant_radius=&unit_length=inches&temperature=70&humidity=35&local_pressure=29.92&pressure=29.92&altitude=900&density=11.4&custom_density=




 
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