FMJ length question

[wakechase]

I am in the process of tinkering with my arrow setup to try and increase my foc. I am currently shooting a 300 spine FMJ @28.75” long with a 125 grain tip pulling 70 lbs with a total weight of 513 grains and a foc of 10%.
Is it counter productive to cut down a FMJ just past the rest to increase speed and help with FOC %. If I were to do that I would be shooting a lighter, shorter and increased foc arrow in theory but then again I’m pretty green with all of this.
Owner at my archery shop said he only shoots arrows for consistent groups and doesn’t worry about foc or paper tuning, that really has thrown me for a loop.

 

[wakechase]

This is the video that has me questioning my set up.

 

[KyleR1985]

I'm not a fan of FMJ's for two reasons: I routinely bent them after going through an animal or hitting another shaft during target practice; and because of the additional weight across the whole arrow getting an arrow with sufficient FOC is difficult.

First choice would be go to with a standard carbon shaft, and install some ethics archery, or other heavy inserts, then use whatever 100 or 125gr broadhead you like. You can stick with 300 spine and likely shoot up to 225-250gr up front total. Any more than that with that arrow length and you probably have to drop to .250.

If forced to work within what you're using now, I don't think it's worth cutting the arrows, stick with what you've got.

What is your goal in increasing FOC?

 

[jmez]

Shoot a faster arrow so the animal doesn't have time to move? Ok. Quit watching the video at that point.

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[Billy Goat]

I think the owner gave you an honest answer. Shoot what shoots best, generally this is an arrow cut 1" past the rest, with foc of 10-15% that falls under a few other parameters for a hunting arrow. If your like me tho you will have to tinker with it, just to realize what's out there from several of the major manufacturers are pretty good recommendations.

 

[wakechase]

I’m not necessarily looking to increase my foc by anything crazy. I would shoot same points and same vanes I guess my main thing would be to have more of an increase in my speed to balance speed and weight. Am I overthinking this all?

 

[KyleR1985]

I’m not necessarily looking to increase my foc by anything crazy. I would shoot same points and same vanes I guess my main thing would be to have more of an increase in my speed to balance speed and weight. Am I overthinking this all?

I generally shoot arrows as short as I can without hitting a rest. There's not really a reason not to if you're building new arrows. There's a few advantages, some he went over in that video.

It's not going to hurt anything. But I don't think you'll make an appreciable difference in speed by cutting off an inch of arrow. If you intend on using a heavier insert/broadhead combination in order to get the weight and FOC up, then this may be a worthwhile modification. But if you're going for speed, this will only slow you down.

 

[wakechase]

I generally shoot arrows as short as I can without hitting a rest. There's not really a reason not to if you're building new arrows. There's a few advantages, some he went over in that video.

It's not going to hurt anything. But I don't think you'll make an appreciable difference in speed by cutting off an inch of arrow. If you intend on using a heavier insert/broadhead combination in order to get the weight and FOC up, then this may be a worthwhile modification. But if you're going for speed, this will only slow you down.

I would be able to cut 3 inches off of my current arrow. They stick out pretty far. I should have stated that but that was my main reasoning behind this all knowing that I had so much excess arrow

 

[KyleR1985]

I would be able to cut 3 inches off of my current arrow. They stick out pretty far. I should have stated that but that was my main reasoning behind this all knowing that I had so much excess arrow

You'll pick up roughly 10fps, assuming all else stays equal. So if your sole purpose is to increase foc and pick up speed, you'll do that. Up to you if the juice is worth the squeeze

 

[Zac]

If you are around 260 fps then I would do it just for speed alone. I like to cut to 28 if possible so that you will know exactly what spine you are dealing with.

 

[ncavi8tor]

I'm also not a fan of the FMJs. Very difficult to get a higher FOC with a high GPI shaft like that. Also they will eventually take a bend and you might not even realize it unless you continuously roll check them. In my opinion the AXIS and/or HEXX are much better shafts.

NC

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[nphunter]

If speed or FOC is a concern at all you purchased the wrong arrows. I personally like to have my arrow shaft even with the front of my riser at full draw, which puts the broadhead out past my fingers which is a good thing.

If your shooting HIT's they are a PITA to get out of an arrow once they are glued in and definitely aren't worth removing just to gain a few feet per second. If you can cut off behind the HIT's it would be doable but still not sure what you will be gaining 6-8fps tops would be my guess. If your really worried about speed you should just sell the FMJ's and build something different.

If your 28.75 and have 3" to spare then I assume you are shooting around 26" draw? Depending on the bow you are probably shooting around 250fps at that weight which IMO is pretty slow for a modern bow. I personally like at least 280fps, I typically aim for 285fps when building my arrows so if I end up heavy I'm still over 280. An Easton Axis would probably be a better platform to start with for a lighter and higher FOC build.

 

[KineKilla]

Shafts cut 3" longer than your draw length are too long in my book. I start with my shafts cut right to the front of the riser and have taken them back to about 1/2" past the rest.

The FMJ's are fine and are a great arrow. If you're worried about having a bent arrow AFTER shooting it through an animal, your priorities might be skewed. That's kind of like being disappointed that your bullet is mushroomed and unusable after it has done its job.

 

[MattB]

I’m not necessarily looking to increase my foc by anything crazy. I would shoot same points and same vanes I guess my main thing would be to have more of an increase in my speed to balance speed and weight. Am I overthinking this all?

Likely yes.

 

[Billy Goat]

Shafts cut 3" longer than your draw length are too long in my book. I start with my shafts cut right to the front of the riser and have taken them back to about 1/2" past the rest.

The FMJ's are fine and are a great arrow. If you're worried about having a bent arrow AFTER shooting it through an animal, your priorities might be skewed. That's kind of like being disappointed that your bullet is mushroomed and unusable after it has done its job.

I have several that are bent that never went through an animal, had a tough broadhead target and I assume I must have bent them pulling them. I also expect an arrow to survive an animal, not that they all do but in the east we get lots of deer tags. Overall they didn't work well for me.

 

[KyleR1985]

Shafts cut 3" longer than your draw length are too long in my book. I start with my shafts cut right to the front of the riser and have taken them back to about 1/2" past the rest.

The FMJ's are fine and are a great arrow. If you're worried about having a bent arrow AFTER shooting it through an animal, your priorities might be skewed. That's kind of like being disappointed that your bullet is mushroomed and unusable after it has done its job.

Reducing consumables any way I can each year helps. Shooting 1000-2000 shots every year in prep for season, it was inevitable i'd bend one pulling it or hitting it with another arrow, or going through 2-3 deer a year. I attempted it for two seasons, and spent an extra hundred bucks and handful of hours figuring out the problem and building the replacements. That's time and money that can be spent better elsewhere. One bullet costs maybe 2.00, and no time.

Is it worth throwing away a dozen arrows? No. But knowing that it's part of the equation may change the math on the next purchase someone makes. I think you'd be hard pressed to come up with an advantage of the FMJ over a standard carbon shaft, with more weight up front to get an equivalent total arrow weight. Costs are within a dollar, components are readily available. I can think of two distinct disadvantages of the FMJ's - lower FOC, and they bend. And if you're not paying attention, and use the proper components, shaft/broadhead joint failures are fairly common with them.

Bottom line for the OP- we agree on making the shafts as short as possible from go. And we agree on using the FMJ's because he's already got them. But frankly, a new post popping up across all of the hunting forums weekly with another hunter frustrated with FMJ's bending, joints failing, or not being able to set the arrows up the way they want, is not random. They're an excellent marketing ploy, and will usually function okay for the average hunter. But they are not without warts, and I suspect if most folks have all of the information when making a purchase, they'll go a different direction. I think that's why I'm making an effort to get the information into the record here - for when someone searches the topic later.

 

[Mighty Mouse]

Is it counter productive to cut down a FMJ just past the rest to increase speed and help with FOC %.

Trimming the arrow won't have much effect on FOC. Gold Tip's FOC calculator predicts that shortening your arrow 3" will increase FOC by 0.7% (9.3% to 10.0%, assuming 12 gn insert, 10 gn nock, and three 2" vanes at 7 gn/each).

If you want to boost your FOC and keep total arrow weight the same, trim the shaft as short as possible and add the reduced shaft weight back in the form of a heavier point, heavier insert, or weight screws. Per GT's calculator, you could get FOC up to ≈12% by trimming 3" and switching to 150 gn points or adding 30 gn of weight screws. I've found GT's FOC calculation to run a bit low (≈0.5%) compared to actual measured FOC, so there's a good chance that those tweaks would put you above 12%.

 

[TSAMP]

Anybody see the FMJ t64 arrow that just came out? It would seem they noticed the FOC concerns and responded with this. Its a 4mm shaft that tapers out to a 6mm shaft out front for better FOC

 

[pirogue]

Don’t overthink it. I have no idea what my FOC is, and am not curious to know, because my bow is tuned and arrows group well. My 28” draw, 60# bow with FMJ, delivered complete pass through at 32 yards on this mud caked bull.

 

[Fisherhahn]

I agree with the don’t overthink it opinion. Personally I would have them cut back 3” just to get the proper fit. Love my fmj’s. My dl is 27” and mine are cut to 25.5”. I never checked but I bet I could have cut them back a bit more and still be past my rest. I too have no idea what my foc is and couldn’t care less. Properly tuned bow and my arrows group well out to the 60yds I practice to and they hit hard. Never had any issues bending and I don’t have to constantly flex and check them to make sure there are no cracks or breaks that send carbon splinters through my hand. Saw it happen to my buddy last year and was not fun getting them out.