Is a 6.5x47 too much recoil for gen 3 add on ?

[silent_varmintor]

Speaking to amate today and he was talking to his mate about my new build and mentioned it was going to be used for NV shooting with Gen 3 add on Archer. His mate reckons it'll be too much recoil for it ?

 

Any thoughts on this lads ?

 

 

 

 

 

Craig

[camo304]

Just tell them at SL what rifle he is using it on, and to make sure the tube is gonna handle the recoil.

[silent_varmintor]

Ill call star light on Monday and see if I can speak with Julian.

[Gandy]

This might sound daft but recoil is influenced by a number of things such as rifle weight and if a mod is used.

 

Just a thought when making the call.

[camo304]

David's post about recoil

I probably should have made a post about this sooner and I have discussed elements of this here previously, from a technical perspective. However recoil damage is starting to become more common in the UK as all kinds of "Pinnacle" tubes and other recent autogating technology shows up, though god only knows where it's coming from. Never the less, since you're all starting to buy it now and I know you're going to have trouble getting it repaired/replaced then I think you should consider some of this before you go whacking your shiny new NV toy on a large rifle.

It's important to understand that NV tube recoil damage is caused by peak acceleration. Many higher powered rifles have a peak acceleration around 400 G's. Modern autogating Gen3 tubes are a bit iffy at anything over 300 G's. People seem to think what they feel in their shoulder is proportional to the recoil of the rifle, but it's not. Peak recoil exists for about 3 milliseconds and the rifle hasn't even started compressing your shoulder at that point.

First, a myth to bust, moderators affect recoil. Well, they do, but not Peak Recoil, which does the damage. The bullet hasn't even reached the moderation by the time you have tube-based recoil damage. Your NV will have been damaged long before any gas escapes the barrel.

So how do you know what's safe? Fortunately there is some interesting published data for just about every cartridge telling us the peak pressure. They are all in PSI and SAAMI release this information.

Some basic physics ( peak recoil is almost entirely piston-physics ) tells us F=MA or to rework that, A=F/M and G's ( G-forces ) = A/9.8

The force on a cartridge face will lead to a certain amount of net force on the entire rifle. This is based on the piston surface area and in this case, the piston is the bullet size.

If a Bullet is 5.56mm, it has an area of 30.9 square millimeters.
One square inch ( PSI is Pounds per Square Inch ) is 635.04 square millimeters.

So, if your cartridge develops 55,000 PSI, then you have 30.9/635.04*55000 pounds of net force acting to accelerate your rifle. Or in this case, 2676 pounds of force accelerating your rifle.

Now google says " 1 pound force = 4.44822162 newtons " and who am I to question that. So your rifle is accelerating with a force of 11,903 newtons. We need newtons, because it's the SI unit for force.

And a final formula is G's = A=F/M/9.8 - So lets assume your rifle mass is 4 Kg.

That's 11903 (F) / 4 (kg) / 9.8 (G)

= 303 G's.... Right on the "safe" limit for modern pinnacle tubes with a halo of around 1.0mm.

If you have a halo less than 0.8mm, don't use it as a rifle-mounted tube at all and if you're between 0.8 and 1.0 be very careful. Weapon mountable tubes should have a halo of 1.25mm so unless yours does, you're playing the risk game anyway.

So weigh up your rifle ( without any dangly bits like tripod - just the fixed items ) and get the weight in Kg. You know your bullet diameter, so multiply by the SAAMI published peak pressure for your total force in pounds, then convert it to newtons.

Then work out how many G's you're expecting.

<300 is considered "low risk" - 300 to 400 is considered "high risk" and >400 is "Don't do it unless you either know what you are doing, or don't mind buying a new tube".

This information is not absolute. It's a guide to help you determine the risk of damaging your NV. Especially if you managed to get your hands on some nice new autogated Gen3. Older Gen3 is tougher, because the autogating increases the likelyhood of damage.

But even then, it's still just probability of damage. Remember that. There is no way of knowing in advance which tubes are more likely to fail even though it's given that lower halo values mean parts are closer together inside the tube and will collide at a much lower recoil level.

And remember that a moderator won't help. There is nothing you can do except to lower the cartridge pressure.

BUT, in simple terms...

> 5.56mm is generally bad.
< 1.0mm is generally bad.
Autogating does not help tube fragility.
More than 300G's should be avoided.
Some dedicated riflescopes have recoil mitigation built in.

I hope this helps I hate to hear of recoil damage happening to anyone. I never posted this much information on this forum, because Gen3 pinnacle and the likes in the UK are very rare, or at least were. I posted tables on the US forums to make it easier for them, but over there everyone on the US forum has an AR15 so it makes the weight part easier.

But if tables would help, I'd be happy to post the recoil data to this forum for different cartridges and rifle weights?

Regards
David